Modular Synthesizer Glossary of Terms

In the field of modular synthesis, you will often hear a lot of unusual terminology, acronyms and abbreviations thrown around. This glossary is an attempt to demystify some of these terms by placing them in the context of modular synthesizers.

Throughout this site, if you see a term with a dashed underline, hover the cursor over it to see the short version of the glossary definition for that term. Click on the term to open its full definition in a new tab.

You can also read the glossary definitions below. Use the search dialog, or click on the letter below to see all terms for that letter. A short version of the definitions will appear. If the definition says to click for more, click on the term’s name (in blue, at the head of its definition) to open a new page with a longer explanation and/or links to other resources.


 

Share This
AJAX progress indicator
Search: (clear)
  • –10 dB
    Most consumer and lower-cost professional audio equipment use a signal level reference known as line level or –10dBV (decibel volts). The most common connectors are RCA (phono) or 3.5mm, although 1/4” is also used; the signal is “unbalanced” (it uses two wires: signal and ground). In the line level standard, a sine wave that varies between +/–0.447 volts is considered to be at –10dBV. By contrast, a typical oscillator signal in a modular synthesizer is +/–5 to +/–8 volts. As a result, you will need either an output module in your modular synth or one heckuva input attenuator on your mixer or recorder to plug your synth into equipment that runs at line level. Similarly, you will need to substantially boost a line level signal to get it up to modular standards to process in your modular synth.
  • (Normalized)
    The power of modular synthesizers is that you can patch a signal to flow the way you prefer through your system. This can also be a time-consuming bummer when you’re just trying to patch a “typical” signal flow. Therefore, some manufacturers have created “semi-modular” synths that have all of these typical connections pre-wired for you, with the important feature that many of these wirings can be overridden by inserting patch cables into the correct jacks. These pre-wired connections are often referred to as being normalled. For example: An internal noise source may normally be connected to one channel of a mixer that appears before the filter, but if you insert a patch cable into a jack usually labeled external input, this “normalled” connection is broken and replaced by your external connection.
  • 0–5v
    Denotes a range of 0 to 5 volts, which is common for gates, triggers, and modulation control voltages in modular synthesizers. Gates and triggers – which initiate events such as new notes – typically rise from 0v to 5v (0 to 10v is also common), with roughly the middle of that onset starting the event. Gates are considered high when held at 5v (or 10v), and then low when they return to 0v. Click for more details.
  • 1 pole
    This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 6 decibels weaker for each octave further away you get from the cutoff frequency. A 6dB/octave filter is often referred to as a “one pole” filter (as each pole of a filter’s design results in 6dB of attenuation), and has a relatively weak effect on the signal going through it. Low Pass Gates (LPGs) typically – but not always – use 1 pole low pass filters, reducing the strength of higher harmonics by 6 decibels for every octave above its cutoff frequency.
  • 1 v/oct
    The most common standard for controlling pitch in a modular synthesizer. Under the system, increasing the voltage going into a VCO (Voltage Controlled Oscillator) 1 volt – say, from 0.5v to 1.5v – would raise its pitch by one octave. Click for more detail.
  • 1/4”
    The most common connector size used for 5U (Moog format) modular synthesizers. These are TS (tip/sleeve) jacks and plugs, similar to guitar and other instrument cables.
  • 1/8”
    Often used to incorrectly describe the connector size commonly used in Eurorack format modules, as well as Buchla audio signals. In fact, Eurorack modules use 3.5mm jacks and plugs (slightly larger than 1/8”); Buchla uses Switchcraft Tini-Jax connectors. Tini-Jax are 3.5mm in diameter, but are slightly different physically from a common 3.5 mm jack. 1/8” plugs would be loose in both of these jacks, so make sure you get 3.5mm connectors ordering parts or cables for these formats.
  • 1 ppqn
    The most common sequencer clock division forwards it one step (pulse) per quarter note. This is often the core sync pulse that is distributed in a modular system, and is either multiplied or divided to create other musical divisions.
  • 1.2 v/oct
    Buchla compatible synths have standardized on the 1.2 volt per octave system, instead of the more common 1 v/oct (see above). With 12 semitones to an octave in Western music, an equally tempered scale would work out to precisely 0.1 volts for a change in pitch of 1 semitone.
  • 2 Pole
    This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 12 decibels weaker for each octave further away you get from the cutoff frequency. A 12dB/octave filter is often referred to as a “two pole” filter (as each pole of a filter’s design results in 6dB of attenuation). Vintage Arp, Korg, and Oberheim instruments often featured 2-pole filters, often resulting in brighter sounds when compared to those with 4-pole instruments.
  • 2’
    Sometimes seen on octave selector switches for oscillators. It refers to the length of an organ pipe. Shorter pipes = higher pitches; 2’ is rarely seen on modular oscillators as it’s rather high in pitch – two octaves above middle C as a starting point. A pipe or setting twice as long (4’) is one octave lower; a pipe twice as long again (8’) is two octaves lower; etc.
  • 2.5 mm
    A common screw thread size used to mount Eurorack modules. This size is most common when using a system of loose nuts that slide along the rails that the modules are attached to.
  • 3 Pole
    This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 18 decibels weaker for each octave further away you get from the cutoff frequency. It is often used a coded shorthand for when someone wants to refer to acid-type bass lines from a TB-303 without mentioning the instrument by name. Click for more details.
  • 3U
    Refers to modules that are 3 rack units (U) high – the Eurorack standard, which is by far the most common modular format today, even though it’s one of the youngest formats.
  • 3 mm
    A common screw thread size used to mount Eurorack modules. This size is most common when using module mounting rails that have been pre-drilled.
  • 3.5 mm
    The standard connector size used for jacks and cables in Eurorack format modular synthesizers. Note that this is slightly larger that 1/8”. Click for more details.
  • 4 Pole
    This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 24 decibels weaker for each octave further away you get from the cutoff frequency. This design is often used in vintage Moog and Roland synths. 4-pole filters are often associated with subjectively fatter, more “round” sounds than 2-pole filters – but generalizations are always dangerous.
  • +4 dB
    This describes the reference used for professional level audio signals. Although it is higher than the more common line level (3.473 volts peak to peak compared to 0.895 volts), it is still not as high as the level used inside many modular synthesizers these days (10 volts ore more peak to peak). As a result, you will often need to attenuate (turn down) a modular signal plugged into a +4dB input, and turn up a +4dB audio signal fed into a modular synth – by a large amount.
  • 4’
    Sometimes seen on octave selector switches on oscillators. It refers to the length of an organ pipe. Shorter pipes = higher pitches; 4’ is the highest octave setting you will see on most oscillators. A pipe or setting twice as long (8’) is one octave lower; a pipe twice as long again (16’) is two octaves lower; etc.
  • 4-40
    A screw thread size occasionally used to mount Eurorack modules. This size is used by Pittsburgh Modular for their cases, for example.
  • 4U
    Refers to modules that are 4U (rack units) high – namely, Buchla and Serge systems, as well as do-it-yourself clones of these modules. Both Buchla and Serge lean toward a more experimental approach to synthesis and music, so some users wear “4U” as a badge of honor that they’re non-conformist and cool. (And they are.)
  • 5U
    Refers to modules that are 5U (rack units) or 8.75” high, which is most often associated with the vintage Moog standard and those who have followed in their footsteps, including Synthesizers.com (Dotcom) and Moon Modular. You will sometimes hear this used interchangeably with MU for Moog Units, which also refers to a standardized width of 2.125” wide per MU. Given that this standard is both historical and physically large, some users “5U” as a badge of honor that they’re traditional and cool. (And the are.) There was also a briefly popular 5U format from MOTM that used a different width and power connection. It has since been discontinued, but there are still diehard MOTM format users today.
  • 6 dB/oct
    This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 6 decibels weaker for each octave further away you get from the cutoff frequency. A 6dB/octave filter is often referred to as a “one pole” filter (as each pole of a filter’s design results in 6dB of attenuation), and has a relatively weak effect on the signal going through it. Low Pass Gates (LPGs) typically – but not always – use 1 pole low pass filters, reducing the strength of higher harmonics by 6 decibels for every octave above its cutoff frequency.
  • 8’
    Sometimes seen on octave selector switches on oscillators. It refers to the length of an organ pipe. Shorter pipes = higher pitches; 8’ is typically associated with middle C. A pipe or setting half as long (4’) is one octave higher; a pipe or setting twice as long (16’) is one octave lower.
  • 10 vpp
    An abbreviation for "10 volts peak to peak" with peak to peak being the difference between the lowest and highest voltage reached during a signal's travels. This is a common voltage range for both audio and modulation signals in a modular synthesizer. The actual range is between –5 and +5 volts. See my diatribe above in the definition of 0–5v: The precise range may be varied to change the depth of their effect, so don’t get too hung up on specific voltage ranges. Pay more attention to whether they vary between 0v and some value, or swing in roughly equal amounts both above and below 0v (as 10vpp does).
  • 12 dB/oct
    This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 12 decibels weaker for each octave further away you get from the cutoff frequency. A 12dB/octave filter is often referred to as a “two pole” filter (as each pole of a filter’s design results in 6dB of attenuation). Vintage Arp, Korg, and Oberheim instruments often featured 2-pole filters, often resulting in brighter sounds when compared to those with 4-pole instruments.
  • 16’
    Sometimes seen on octave selector switches on oscillators. It refers to the length of an organ pipe. Longer pipes = lower pitches; 16’ is in the mid-bass range. A pipe or setting half as long (8’) is one octave higher; a pipe half as long again (4’) is two octaves higher; etc.
  • 18 dB/oct
    This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 18 decibels weaker for each octave further away you get from the cutoff frequency. It is often used a coded shorthand for when someone wants to refer to acid-type bass lines from a TB-303 without mentioning the instrument by name. Click for more details.
  • 24 ppqn
    A common master clock division used in MIDI, DIN sync, and other systems common to electronic music and synthesizers. It means internally, 24 subdivisions of time are counted for every quarter note at the current tempo. This fast internal clock can then be divided down to create sixteenth notes (÷6), eighth notes (÷12), eight note triplets (÷8), etc.
  • 24 dB/oct
    This format of numbers and abbreviations (dB/oct = decibels per octave) is often used to refer to the frequency response behavior of a filter. A filter typically has a cutoff or corner frequency it is tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that its loudness is multiples of 24 decibels weaker for each octave further away you get from the cutoff frequency. This design is often used in vintage Moog and Roland synths. 4-pole filters are often associated with subjectively fatter, more “round” sounds than 2-pole filters – but generalizations are always dangerous.
  • 32’
    Sometimes seen on octave selector switches on oscillators. It refers to the length of an organ pipe. Longer pipes = lower pitches; 32’ is the lowest setting you will see and is getting into earthquake territory. A pipe or setting half as long (16’) is one octave higher; a pipe half as long again (8’) is two octaves higher; etc.
  • A-440
    This is the frequency in hertz (cycles per second) of the A above Middle C. It is often used as a tuning reference.
  • AC
    In modular terms, AC refers to a voltage that alternates between positive and negative values – such as the output of an oscillator.
  • AC Coupled
    An AC coupled input attempts to remove any constant DC voltage going through it. This is useful if have an audio signal (such as the output of an oscillator) which is AC in nature, and you want to remove any accidental DC offset that might have crept into it. These offsets can cause one half of the AC waveform to clip prematurely, or can cause clicks at the start and end of envelopes or mutes. However, this coupling can mildly distort a wave going through it, as in essence AC coupling is a high pass filter that is attempting to remove very low frequency components. Click through for a link to a good technical article on the subject.
  • Active Multiple
    Quite often you need to split or copy a signal to send to more than one destination. This is commonly done with a multiple, where you plug one source in, and then plug in additional patch cables to go off to multiple destinations. An active or buffered multiple is one that includes a buffer circuit between the input and output, making sure the signal does not lose its strength or integrity by being split too many times, and that no funny business happening on one of the outputs affects any of the other connections. Some modules have good buffering built into their outputs, and can drive multiple modules without issue. But if you try to use a passive mult to connect to, say, three oscillators, and you realize the tracking isn't very good (they quickly go out of tune as you go up and down the scale), then you need a buffered mult instead. Click through for more technical details.
  • AD
    Shorthand for a two-stage Attack/Decay envelope. This simple envelope shape raises from 0 volts to its maximum level (typically 5, 8, or perhaps 10 volts) at a speed defined by its Attack parameter, and then immediately falls back to 0 volts at a rate defined by its Decay parameter. A variation on this is the AHD envelope: After finishing the Attack stage, it holds at the maximum level for a specified amount of time (in contrast to an AR envelope, which holds at the maximum level for as long as the note on gate is high), and then decays back to zero. I have heard there are some envelopes that a hybrid of AHD and AR in that they hold the maximum level for either the defined Hold time or the as long as the incoming gate is high; let me know in the comments if you have a specific example.
  • Additive Synthesis
    One of the main properties that make a sound unique is the mixture of harmonics – pure component frequencies – that it is built from. Additive synthesis is a technique that gives you direct control over each of those component harmonics, allowing you to directly dial in the mix you want. As immediate and intuitive as that sounds on paper (or on screen), in reality it takes a lot of work to craft the correct mixture to recreate another sound, especially since the strength of each harmonic usually varies over time. Additive synthesis oscillators are relatively rare in modular synths; two examples are the Verbos Harmonic Oscillator and the Make Noise tELHARMONIC.
  • ADSR
    An envelope generator with four stages: Attack, Decay, Sustain, and Release. When this envelope generator receives a gate input, it typically starts at 0 volts (which is the equivalent of silence when connected to a Voltage Controlled Amplifier, or the lowest frequency when connected to a voltage controlled filter or oscillator) and raises to the maximum voltage it can output (typically 5 to 10 volts depending on system; it can often be set with an output level control) over a time set by the Attack control. Once it reaches that level, the output voltage immediately starts dropping to speed set by the Decay control it until it reaches the voltage set by the Sustain control. If the input gate is still active, this level is maintained until the gate goes back to 0 volts (usually because you released the key on a controlling keyboard, etc.). At that time, the output voltage then starts dropping back to 0 volts at the rate set by the Release control. Click for more about variations in ADSR behaviors.
  • AFG
    The AFG (Audio Frequency Generator) is a very full-featured analog oscillator released by Livewire Electronics. It has since been discontinued, but refurbished B-stock units come up for sale every now and then. The expansion modules were, to the best of my knowledge, never released (at least not widely). Yes, it uses two power connectors. No, I haven't seen a manual for it yet.
  • Aftertouch
    Some keyboards measure how hard you press down on the keys, and convert this to a voltage (or other control signal such as MIDI, which can then be converted into a control voltage) that you can use to add expression to a note, such as adding vibrato or opening the filter wider. Monophonic aftertouch measures one pressure value for the entire keyboard, regardless of which key(s) you are pressing; polyphonic aftertouch produces a signal for each individual key. Important trivia: Touch plate keyboards actually measure the surface area of the skin touching them rather than pressure or force – so you can increase or decrease the aftertouch amount by rolling between the tip and length of your finger.
  • AHDSR
    This is a slightly fancier ADSR envelope that holds the voltage typically at its maximum value for a specified time after the attack is done rising and before the decay starts falling.
  • Aliasing
    If you play back a digital audio file where half of the sample rate is an audible pitch, you will also hear a mirror image of the sound’s harmonic content reproduced started at that half-sample-rate pivot (unless some excellent filtering has taken place). Click for more details.
  • Alternating Current
    In modular terms, AC refers to a voltage that alternates between positive and negative values – such as the output of an oscillator.
  • AM
    Amplitude Modulation (AM) is the name given the to the technique of varying the amplitude or loudness of one signal known as the carrier (typically an audio signal, swinging both above and below 0 volts) with a second signal called the modulator. In the typical amplitude modulation (AM) scenario, a low frequency oscillator with a positive voltage (say, between 0v and 5v, or maybe something smaller such as between 1v and 2v) is fed into the control input of a voltage controlled amplifier to add vibrato to an audio signal passing through it. Technically, this is known as a two-quadrant multiplier or modulator, as any negative swings in the modulation signal are ignored; when patching tremolo, you may need to make sure an offset voltage is being added to your LFO to make sure the sound doesn’t cut out on the lower excursions of the LFO’s waveform. Click for more detail.
  • Amplitude Modulation
    Amplitude Modulation (AM) is the name given the to the technique of varying the amplitude or loudness of one signal known as the carrier (typically an audio signal, swinging both above and below 0 volts) with a second signal called the modulator. In the typical amplitude modulation (AM) scenario, a low frequency oscillator with a positive voltage (say, between 0v and 5v, or maybe something smaller such as between 1v and 2v) is fed into the control input of a voltage controlled amplifier to add vibrato to an audio signal passing through it. Technically, this is known as a two-quadrant multiplier or modulator, as any negative swings in the modulation signal are ignored; when patching tremolo, you may need to make sure an offset voltage is being added to your LFO to make sure the sound doesn’t cut out on the lower excursions of the LFO’s waveform. Click for more detail.
  • Analog
    The term analog implies a signal is continuously variable, compared to digital where a signal has been converted into discrete numbers. In the land of modular synthesizers, analog refers to a circuit design that has no digital (or at least, computer-based) components – instead, it does all of its processing using transistors, diodes, capacitors, and the such rather than CPUs and DSPs. Click for some editorializing.
  • Analog Shift Register
    An Analog Shift Register (ASR) is a cross between a Sample & Hold module and a Bucket Brigade Delay (assuming you already know how those work). When initially triggered, it samples the incoming voltage, and presents that at its first output. On the second trigger, the incoming voltage is sampled again with this new voltage presented at the first output, while the original voltage is now moved to a second output. This game of "telephone" is passed along for as many stages as the ASR has – traditionally three or four. Click through for more history as well as links and sources.
  • AND function
    One of the most common Boolean or binary logic functions, AND says only output a gate on signal if all of the inputs see “high” gate signals (i.e. input 1 and input 2 etc. all have gate ons). A NAND function has an inverted output: The output would be low if both inputs were high, but otherwise would be high.
  • AR
    The two-stage Attack/Release envelope raises from 0 volts to its maximum level (usually 5, 8, or maybe even 10 volts) at a rate set by its Attack parameter, and then stays at that value for as long as the gate signal fed into the envelope generator stays high. Then when the gate signal goes back to zero, the envelope's output also falls back to zero at a rate set by its Release parameter. (There is a separate type of envelope known as an AHD – Attack/Hold/Decay – where you specify a fixed time for the level to stay at its maximum, rather than pay attention to the gate signal.)
  • Arpeggiator
    Putting on our music theory hat for a second, an arpeggio is a type of “broken chord” where the notes are played individually rather than all at once. An arpeggiator – usually built into a keyboard, or a device inserted between your keyboard and sound module – makes it easier for you to play arpeggios: You just hold down the notes of the chord, and it automatically plays the notes one at a time, over and over again, like a step sequencer you can program on the fly just by holding down a chord. Good arpeggiators have options for different patterns (up, down, back and forth, random, etc.), and even a latch or hold where it will keep doing this even after you’ve released the keys.
  • ASR
    An Analog Shift Register (ASR) is a cross between a Sample & Hold module and a Bucket Brigade Delay (assuming you already know how those work). When initially triggered, it samples the incoming voltage, and presents that at its first output. On the second trigger, the incoming voltage is sampled again with this new voltage presented at the first output, while the original voltage is now moved to a second output. This game of "telephone" is passed along for as many stages as the ASR has – traditionally three or four. Click through for more history as well as links and sources.
  • Attack
    This usually refers to the first stage of an envelope that occurs at the onset of a note, as it rises from 0 volts (silence when if controlling an amplifier module) to typically the value of maximum loudness. Percussive and plucked sounds have very fast attacks; slow, languid wind or string instrument phrases may have long attacks.
  • Attack/Decay
    Shorthand for a two-stage Attack/Decay envelope. This simple envelope shape raises from 0 volts to its maximum level (typically 5, 8, or perhaps 10 volts) at a speed defined by its Attack parameter, and then immediately falls back to 0 volts at a rate defined by its Decay parameter. A variation on this is the AHD envelope: After finishing the Attack stage, it holds at the maximum level for a specified amount of time (in contrast to an AR envelope, which holds at the maximum level for as long as the note on gate is high), and then decays back to zero. I have heard there are some envelopes that a hybrid of AHD and AR in that they hold the maximum level for either the defined Hold time or the as long as the incoming gate is high; let me know in the comments if you have a specific example.
  • Attack/Decay/Sustain/Release
    An envelope generator with four stages: Attack, Decay, Sustain, and Release. When this envelope generator receives a gate input, it typically starts at 0 volts (which is the equivalent of silence when connected to a Voltage Controlled Amplifier, or the lowest frequency when connected to a voltage controlled filter or oscillator) and raises to the maximum voltage it can output (typically 5 to 10 volts depending on system; it can often be set with an output level control) over a time set by the Attack control. Once it reaches that level, the output voltage immediately starts dropping to speed set by the Decay control it until it reaches the voltage set by the Sustain control. If the input gate is still active, this level is maintained until the gate goes back to 0 volts (usually because you released the key on a controlling keyboard, etc.). At that time, the output voltage then starts dropping back to 0 volts at the rate set by the Release control. Click for more about variations in ADSR behaviors.
  • Attack/Hold/Decay/Sustain/Release
    This is a slightly fancier ADSR envelope that holds the voltage typically at its maximum value for a specified time after the attack is done rising and before the decay starts falling.
  • Attack/Release
    The two-stage Attack/Release envelope raises from 0 volts to its maximum level (usually 5, 8, or maybe even 10 volts) at a rate set by its Attack parameter, and then stays at that value for as long as the gate signal fed into the envelope generator stays high. Then when the gate signal goes back to zero, the envelope's output also falls back to zero at a rate set by its Release parameter. (There is a separate type of envelope known as an AHD – Attack/Hold/Decay – where you specify a fixed time for the level to stay at its maximum, rather than pay attention to the gate signal.)
  • Attenuator
    A control that can reduce the strength of a signal or voltage going through it.
  • Attenuverter
    A special version of an attenuator that can also invert the polarity of the signal or voltage going through it. Most attenuverters use pass through no signal at their center position; as you turn them clockwise, you turn up the normal version of the signal; as you turn them counterclockwise, they turn up an inverted version of the signal. Some attenuverters are a normal attenuator with a polarity switch added on.
  • Audio Frequency Generator
    The AFG (Audio Frequency Generator) is a very full-featured analog oscillator released by Livewire Electronics. It has since been discontinued, but refurbished B-stock units come up for sale every now and then. The expansion modules were, to the best of my knowledge, never released (at least not widely). Yes, it uses two power connectors. No, I haven't seen a manual for it yet.
  • Balanced Audio
    This refers to a system where three wires are used to carry an audio signal: one is the ground (the 0 volt reference), the second carries the audio signal as it varies above and below 0v, and the third carries an inverted copy of the audio signal that goes negative while the original is going positive. Balanced audio usually implies a reference signal level of +4dB (higher than line level; still lower than most modular synths), although microphone signals – much weaker by comparison, and therefore more susceptible to outside noise – are almost always balanced as well. Modular synths tend to use unbalanced audio for their internal signals. If you require a balanced output (or input), you need a special module that converts between balanced and unbalanced audio, plus does any necessary level matching.
  • Balanced Modulator
    Balanced or ring modulation is a special type of amplitude modulation, where one bipolar (swinging both above and below 0 volts) signal – the modulator – is used to vary the amplitude of a second bipolar signal, known as the carrier. The modulator’s frequency is both added to and subtracted from the carrier’s frequency; the resulting harmonics replace the original carrier and modulator. Click for more details.
  • Banana
    An alternate type of connector (https://en.wikipedia.org/wiki/Banana_connector) used by 4U systems such as Buchla (control voltages) and Serge (both control and audio). These cables have only one wire, so they carry only the signal, relying on the module panels and chassis of the system to provide the ground reference. Banana connectors have an advantage in that they are usually “stackable” meaning you can plug a one jack into the back of another, providing a passive multiple.
  • Bandpass Filter
    A bandpass filter (BPF) leaves the harmonics around the center, corner or cutoff frequency untouched, and attenuates those above and below the center frequency. The further away you get from the center, the more they are attenuated, based on the number of poles in the filter, with each pole equalling 6 decibels of attenuation for each octave you get away from that center.
  • Bark Scale
    The human auditory (hearing) system can be thought of as consisting of a series of bandpass filters. Interestingly, the spacing of these filters do not strictly follow either a linear frequency scale or a logarithmic musical scale. The Bark Scale is an attempt to determine what the center frequency and bandwidth of those "hearing filters" are (known as critical bands). Click through for a few more details and technical links.
  • BBD
    An early design for an echo or delay effect where the input audio would be sampled as an analog voltage, and held for a brief moment. Then at the next above-audio sample rate clock pulse, this voltage would get passed to the next sample and hold (bucket) in the circuit, while a new level was sampled. Bucket brigade delays (BBDs) usually have numbers of stages or buckets that are powers of two (256, 512, 1024, 2048, etc.); the delay length is determined by the number of stages multiplied by the time interval between samples. Click for more about the downsides of BBDs.
  • Beating
    When two oscillators are tuned to very nearly – but not quite – the same frequency, the difference between them causes an interference pattern known as beating. When the difference in frequency is below the audio rate, this can sound like a tremolo applied to the loudness of the combined sound. Click for more.
  • Beats Per Minute
    BPM (beats per minute) is the most common way of stating tempo: How many beats (typically, quarter notes) should be counted every minute. A tempo of 120 beats per minute means there would be two beats every second (120 beats/minute x 1 minute/60 seconds = 2).
  • Berlin School
    A particular style of electronic music popularized by the likes of Tangerine Dream and Klaus Schulze based on analog synthesizers, heavy on repetitive sequences and floating chords or drones with solos played on top. More recent versions of Berlin School music can be heard from Node and Red Shift.
  • Binary
    A cornerstone of digital systems is the binary counting method, where each digit can have only two different values: 0 or 1; off or on; low or high. A binary signal can only have one of these two states. Therefore, a gate or trigger signal in a modular synth – even if generated by analog circuitry – could be referred to as a binary type signal. See the entry for Boolean for things you can do with binary signals like gates and divided clocks.
  • Bipolar
    No, not a disorder that afflicts synthesists who have a love/hate relationship with their instrument! A voltage that can range both above and below zero is referred to as bipolar. Some modulation signals inside a modular synth – such as vibrato (varying the pitch of an oscillator both above and below the note it is supposed to be playing) – are bipolar in nature.
  • Blue Noise
    Technically, a type of noise whose power density (spectral loudness) increases 3 dB per octave with increasing frequency. It has a very “hissy” characteristic, lacking in bass. Click for a link with examples.
  • Boolean
    Boolean is a fancy way of saying binary. Boolean logic can have only two states: high or low; 1 or 0; on or off. Click for more details.
  • BPF
    A bandpass filter (BPF) leaves the harmonics around the center, corner or cutoff frequency untouched, and attenuates those above and below the center frequency. The further away you get from the center, the more they are attenuated, based on the number of poles in the filter, with each pole equalling 6 decibels of attenuation for each octave you get away from that center.
  • BPM
    BPM (beats per minute) is the most common way of stating tempo: How many beats (typically, quarter notes) should be counted every minute. A tempo of 120 beats per minute means there would be two beats every second (120 beats/minute x 1 minute/60 seconds = 2).
  • Brown Note
    Bass, how low can you go? The mythical brown note is so low (some say 5-9 Hz – well below human hearing) that it sets up a resonance in that body that causes a person to lose control of their bowels.
  • Brownian Noise
    Also referred to as brown noise, technically it’s a type of noise whose power density (spectral loudness) decreases 6 dB per octave with increasing frequency. It has a bass-heavy sound, akin to the sound of the surf at a distance. It can also be used a slowly changing random control voltage or modulation signal, instead of as an audio source.
  • Bucket Brigade Delay
    An early design for an echo or delay effect where the input audio would be sampled as an analog voltage, and held for a brief moment. Then at the next above-audio sample rate clock pulse, this voltage would get passed to the next sample and hold (bucket) in the circuit, while a new level was sampled. Bucket brigade delays (BBDs) usually have numbers of stages or buckets that are powers of two (256, 512, 1024, 2048, etc.); the delay length is determined by the number of stages multiplied by the time interval between samples. Click for more about the downsides of BBDs.
  • Buffered Multiple
    Quite often you need to split or copy a signal to send to more than one destination. This is commonly done with a multiple, where you plug one source in, and then plug in additional patch cables to go off to multiple destinations. An active or buffered multiple is one that includes a buffer circuit between the input and output, making sure the signal does not lose its strength or integrity by being split too many times, and that no funny business happening on one of the outputs affects any of the other connections. Some modules have good buffering built into their outputs, and can drive multiple modules without issue. But if you try to use a passive mult to connect to, say, three oscillators, and you realize the tracking isn't very good (they quickly go out of tune as you go up and down the scale), then you need a buffered mult instead. Click through for more technical details.
  • Bus Board
    This simple circuit board takes the output of your modular system's power supply and creates multiple copies of it, routed to connectors that go to your individual modules. Click through for advice on finding the best bus board designs, and how to connect them.
  • Carrier
    There are a few different synthesis techniques where one usually audio-rate signal varies another audio signal. For example, in frequency modulation, a second signal (called the modulator) varies the frequency (pitch) of the main signal, called the carrier. More specifics are described in the entries on frequency modulation and amplitude modulation.
  • CCW
    Counter-clockwise, usually in the context of rotating a control the left (in the opposite direction of how a clock's hands move).
  • Cent
    When tuning instruments, a semitone is divided into 100 units called cents; there are 1200 cents per octave (100 x 12 semitones). When one oscillator is detuned compared to another, the difference in their frequencies is sometimes measured in cents.
  • Chaotic
    Believe it or not, chaotic does not mean completely random to mathematicians. Chaos theory deals with systems that are random within certain boundaries – such as the path of a wobbling wheel or the frequency of a dripping faucet. Although they are not out of control, neither are they completely predictable. In synthesis, a chaotic system usually refers to a modulation generator that is similar to a low frequency oscillator, but which has unpredictable wobbles or glitches in an otherwise loosely or occasionally repetitive pattern. It can also refer to bursts of triggers that do not follow musical divisions.
  • Chorus
    A type of signal processor that makes a single audio signal sounds like multiple sources, playing in almost-unison with some slight detuning. This is done by delaying a copy of the original signal, and then varying the amount of delay to create animation in the final mix between the two.
  • Class Compliant
    This refers to a device that is "plug and play" – it can be plugged directly into a computer or other host and immediately be recognized without additional drivers needing to be installed. This comes up in the modular world with MIDI to CV/Gate interfaces that use USB: If your converter is a USB Host, and you plug a class compliant USB Device such as a controller keyboard or fader panel into it, the converter will recognize it. Click through for more on USB Hosts and Devices.
  • Clip
    All active electronic circuits have a limit on how strong of a signal can pass through them. These limits are often associated with the positive and negative power supply levels. If the signal attempts to go beyond these limits, they instead get chopped or clipped off at that limit. For example, an input voltage of +12 volts may get through without alteration, but +13 volts at the input would come out as 12 volts. This clipping causes distortion in the waveform, usually adding higher harmonics (such as a harsh buzz). Different circuits enter clipping in different ways – some may have a bit of rounding off before they reach that flat threshold; this is referred to as soft clipping and is often desirable as it can be less harsh.
  • Clock
    Usually refers to the main rhythmic pulse in a system. Often, the clock pulse is much faster than anything it might drive, such as a sequencer or LFO. The most common clock rate is 24 ppqn (pulses per quarter note), as is the case with MIDI clocks and DIN Sync. However, a trigger that drives a sequencer forward one note at a time may also be called the “clock” in a system. Indeed, there are modules that create divisions and multiplications of the main clock to generate new clock signals with a relationship to the main clock.
  • Clockwise
    Clockwise, as in rotating a control the the right – in the same direction as a clock's hands move.
  • Comparator
    An electrical device that compares the level of one voltage to a second. That second voltage may be a second input on a comparator synth module, or may be set with a knob or internal reference voltage. Most often, a comparator outputs a gate signal that goes high when the first signal is higher than the second (or vice versa), and which goes low when the first signal is lower than the second. At audio rates, it converts an input waveform into a square or pulse wave, with the second signal setting when the new waveform goes high or low in voltage.
  • Complex Oscillator
    This module typically has a pair of oscillators behind one panel that is prewired where one oscillator modulates the other’s frequency (known as Frequency Modulation or FM synthesis); some also allow you to quickly switch them so that the first modulates the amplitude of the second, or some other variation. They may also have waveshapers built in. They are based on a popular module created by Buchla, which is a standard of the “West Coast” approach to synthesis.
  • Control Voltage
    The concept of control voltage (CV) is at the very root of modular synthesizer. The general idea is that analog voltage levels are used control functions and parameters of a module. For example, one control voltage may determine the pitch played by an oscillator; a second control voltage may determine how loud that signal is after it’s passed through a voltage-controlled amplifier. CV is the most common shorthand to refer to control voltage – for example, when a synthesizer module says it features “CV over the filter’s resonance,” that means there is a control voltage input to control the amount of resonance (feedback) – not just the customary knob on the front panel.
  • Control Voltage Processor
    CVP is the abbreviation for a module that allows processing of the voltage going through it – such as amplifying or attenuating it, offsetting it in a positive or negative direction, introducing slew (slurring of changes in voltage), and possibly other functions such as deriving a gate signal from an incoming voltage by running it through a comparator. Make Noise’s Maths is perhaps the most well known control voltage processor out there; you will also find some modules with CVP specifically in their name. Regardless, it’s good to have one or more of this type of module in your system to help massage voltages to get them to do what you want (or to teach them new tricks).
  • Corner Frequency
    The cutoff or corner frequency of a filter is the point at which is starts filtering. For example, if a low-pass filter has a corner frequency of 500 Hz (cycles per second), all harmonics or other sound components below 500 Hz will be allowed through untouched, and all harmonics above 500 Hz will be “filtered” – reduced in loudness – the further above 500Hz you go.
  • Counter Clockwise
    Counter-clockwise, usually in the context of rotating a control the left (in the opposite direction of how a clock's hands move).
  • Cutoff Frequency
    The cutoff or corner frequency of a filter is the point at which is starts filtering. For example, if a low-pass filter has a corner frequency of 500 Hz (cycles per second), all harmonics or other sound components below 500 Hz will be allowed through untouched, and all harmonics above 500 Hz will be “filtered” – reduced in loudness – the further above 500Hz you go.
  • CV
    The concept of control voltage (CV) is at the very root of modular synthesizer. The general idea is that analog voltage levels are used control functions and parameters of a module. For example, one control voltage may determine the pitch played by an oscillator; a second control voltage may determine how loud that signal is after it’s passed through a voltage-controlled amplifier. CV is the most common shorthand to refer to control voltage – for example, when a synthesizer module says it features “CV over the filter’s resonance,” that means there is a control voltage input to control the amount of resonance (feedback) – not just the customary knob on the front panel.
  • CV/Gate
    This is the shorthand to say a synthesizer may be controlled by voltages (see control voltage above) – usually for pitch – and gate signals to indicate when a note is “on.” An increasing number of controller keyboards are including CV/Gate output in addition to the customary MIDI (Musical Instrument Digital Interface), making them much easier to connect to a modular synthesizer, as no additional MIDI to CV interface is required.
  • CVP
    CVP is the abbreviation for a module that allows processing of the voltage going through it – such as amplifying or attenuating it, offsetting it in a positive or negative direction, introducing slew (slurring of changes in voltage), and possibly other functions such as deriving a gate signal from an incoming voltage by running it through a comparator. Make Noise’s Maths is perhaps the most well known control voltage processor out there; you will also find some modules with CVP specifically in their name. Regardless, it’s good to have one or more of this type of module in your system to help massage voltages to get them to do what you want (or to teach them new tricks).
  • CW
    Clockwise, as in rotating a control the the right – in the same direction as a clock's hands move.
  • DADSR
    This is a slightly fancier take on the standard ADSR envelope generator that introduces an initial timed delay before the initial attack stage (rising from 0 to a peak level) begins. One patch idea is to route this type of envelope to a low pass filter cutoff, so there’s initially a muted, filtered sound when the note starts, and then after a pause it starts to swell into a brighter, fuller sound.
  • DC
    In modular terms, DC refers to a voltage that tends to stay at one steady level for awhile, such as a gate output that switches between 0v when a note is off and 5 or 10v when a note is on. It can also refer to a slowly changing voltage, such as an envelope.
  • DC Coupled
    When a module says its inputs are DC Coupled, that means it can accept DC voltages (constant or slowly changing voltages) and pass them through unaltered. This is important if, for example, you want to use a VCA to control the amplitude of an envelope going through it: You would need one that was DC coupled, as an AC coupled input would try to remove the DC component of the signal (such as its sustain level) and return it to 0v. Click through for a link to a good technical article on the subject.
  • DCO
    A DCO (Digitally Controlled Oscillator) is a hybrid design for an analog oscillator that – instead of using a voltage level to determine the pitch of the oscillator – uses a digital device such as a counter to determine the length of each waveform cycle and therefore the pitch. On the plus side, tuning is very stable, unlike some all-analog designs. On the minus side, there are no imperfections in pitch that cause subtle detuning (and therefore the perception of “fatness”) when using more than oscillator per voice. Click for more details.
  • Decay
    In general, decay refers to a voltage or overall level dropping down from some high point, such as the decay stage of an envelope generator. A real-world analogy is that after you initially strike a drum or pluck a string, it decays in volume from its initial loudness eventually all the way to silence. It can also refer to the tail of a reverb or echo effect where the sound dies away over time.
  • Delay
    You all know what the word delay means in the normal world; it can appear in different forms inside a modular synth. For example, it can refer to the spacing between repeats in an echo; that’s why an echo device is often known as a “delay” effect. It can also refer to a programmable amount of time you delay a signal, such as a gate, trigger, or initial stage of an envelope so a note would start later than it was actually played.
  • Delay/Attack/Decay/Sustain/Release
    This is a slightly fancier take on the standard ADSR envelope generator that introduces an initial timed delay before the initial attack stage (rising from 0 to a peak level) begins. One patch idea is to route this type of envelope to a low pass filter cutoff, so there’s initially a muted, filtered sound when the note starts, and then after a pause it starts to swell into a brighter, fuller sound.
  • Detune
    If you have two oscillators tuned to exactly the same frequency – and I mean, exactly the same frequency – there’s not much point in having more than one oscillator. However, when you change the tuning of one ever so slightly – in other words, detune it – you will start to hear interesting interactions between the two, often referred to as chorusing or beating. The result tends to be more interesting and “full” – and a bit more natural, as two singers or instruments can rarely hit exactly the same note.
  • Difference
    A fancy way of saying you subtracted on control voltage from another. It can also be applied to audio or harmonics.
  • Digital
    There was a time when digital (referring to circuitry based around binary logic, computers, and the such compared to the old-fashioned transistors, op amps, capacitors, and other bits that make up analog circuitry) was a dirty word among synthesists. The assumption was digital techniques created sounds that were more sterile, brittle, and abrasive – and just not as “authentic.” Today, digital circuitry is embraced in synthesizers, including modular systems. Although analog will always hold a special place in our hearts, a well-implemented digital circuit can sound just as good as an analog one, while digital signal processing and programming can create a wider range of sounds than most analog circuitry.
  • Digitally Controlled Oscillator
    A DCO (Digitally Controlled Oscillator) is a hybrid design for an analog oscillator that – instead of using a voltage level to determine the pitch of the oscillator – uses a digital device such as a counter to determine the length of each waveform cycle and therefore the pitch. On the plus side, tuning is very stable, unlike some all-analog designs. On the minus side, there are no imperfections in pitch that cause subtle detuning (and therefore the perception of “fatness”) when using more than oscillator per voice. Click for more details.
  • DIN Sync
    A clock signal for controlling the tempo of sequencers, arpeggiators, and drum machines, distributed using cables with DIN-style connectors (yes, just like old-fashioned MIDI connectors, but DIN Sync is even older). Roland pioneered this standard, which included sending 24 pulses per quarter note (PPQN), giving rise to the alternate name Sync24. Korg equipment used a variation of this running at 48 pulses per quarter note, also known as Sync48. DIN Sync is still a popular way of sending a clock signal to a modular synth today, especially when interfacing with other vintage synthesizers, sequencers, and drum machines.
  • Diode Ladder Filter
    This is a filter design most often associated with the Roland TB-303 Bass Line, which is known for its rubbery sound with eager resonance.
  • Direct Current
    In modular terms, DC refers to a voltage that tends to stay at one steady level for awhile, such as a gate output that switches between 0v when a note is off and 5 or 10v when a note is on. It can also refer to a slowly changing voltage, such as an envelope.
  • dry
    A sound with no effects is referred to as "dry"; a sound with effects (such as reverb) mixed is referred to as "wet." Effects units or mixers often have wet/dry mix amounts that set the ratio between the original, unprocessed sound and the fully-effected sound.
  • Duophonic
    Duophonic means two "voices." Most early synths (including modular systems) are monophonic, which means they can play only one note at a time; some instruments have enough oscillators, filters, envelopes, and amplifiers that they could play two separate notes as once. Some MIDI interfaces for modular synths include duophonic modes so you can patch up and control two separate voices from your keyboard. Some users play fast and loose with terms such as duophonic, monophonic, and polyphonic; some really care about precise usage - click through for a link by an authoritative article by Marc Doty on the subject.
  • Duration
    Duration is another way of saying length. A clock pulse or a gate signal that is “high” for a certain amount of time – say, 100 msec – is said to have a duration of 100 msec. The length of time you hold a note down, or the length of a step in a sequence, is also called its duration.
  • East Coast Synthesis
    This blanket term is applied to most common synthesizer configuration pioneered by East Coast based companies such as Moog, Arp, and EML (as well as “Far East” companies such as Roland and Korg) where one or more oscillators producing waveforms with rich harmonic content (such as a sawtooth or square wave) are fed into a filter that removes some of those harmonics, and then onto an amplifier to shape the loudness of a note. This approach is also often known as subtractive synthesis, as the filter reduces (subtracts) harmonics that came from the oscillators. East Coast synthesizers also regularly have organ-style black & white keyboards, and four stage ADSR type envelopes. Today it's common to mix both East Coast and West Coast approaches in the same system.
  • Effect Loop
    Sometimes you might want to send a signal outside your modular system, process it through an external effects device, and bring it back into your modular for more processing. This going out/coming back in is referred to as an effect loop. The trick with modular synths is that their internal signal levels tend to be much higher than those used by external effect equipment, so a modular effect loop will usually have level matching circuitry as well.
  • EG
    The envelope generator (EG) module is used to shape the loudness or dynamics of a note when connected to a VCA (Voltage Controlled Amplifier), as well as how its frequency content or timbre changes over time when connected to a VCF (Voltage Controlled Filter). To do this, and envelope generator creates a voltage that typically rises from zero volts to some maximum level, and back down again. You control how long this takes, usually in various stages: an attack stage as it goes from zero to max, a decay stage as if falls back down from maximum to either zero (in the case of an AD, or Attack/Decay envelope) or an intermediate level known as the sustain, and then (usually after a key has been released and the corresponding gate signal has gone back to zero) from the sustain level back to zero over a duration known as its release.
  • Emphasis
    This word can have two meanings. In a normal audio context, it usually means some form of high frequency boost, as emphasizing the higher harmonics can add clarity to a tone and help distinguish it from another. In synthesizers, emphasis usually means the Q or resonance setting on a filter, as increasing this setting boosts (emphasizes) the harmonics at the cutoff or corner frequency.
  • Envelope
    In general, the term envelope refers to the “shape” of a sound – the contour of how it gets louder and then softer over time. Sometimes envelope is used as shorthand for envelope generator. Envelopes are often described by the stages they have in them – for example, an ADSR envelope has attack, decay, sustain, and release stages. This glossary contains definitions for the most common envelope types.
  • Envelope Follower
    This module follows the loudness contour of a sound, and outputs a voltage that corresponds to how that loudness changes. They tend to perform some smoothing on this signal so that it’s not too nervous or jumpy in nature. Envelope followers often also have a gate output that goes high when the loudness of the input signal went over a certain level, and low when it falls back below that level. Click for what to look out for an envelope follower.
  • Envelope Generator
    The envelope generator (EG) module is used to shape the loudness or dynamics of a note when connected to a VCA (Voltage Controlled Amplifier), as well as how its frequency content or timbre changes over time when connected to a VCF (Voltage Controlled Filter). To do this, and envelope generator creates a voltage that typically rises from zero volts to some maximum level, and back down again. You control how long this takes, usually in various stages: an attack stage as it goes from zero to max, a decay stage as if falls back down from maximum to either zero (in the case of an AD, or Attack/Decay envelope) or an intermediate level known as the sustain, and then (usually after a key has been released and the corresponding gate signal has gone back to zero) from the sustain level back to zero over a duration known as its release.
  • Envelope Tracking
    This describes the main action of an envelope follower: a module or section of a module that follows the loudness of a signal and outputs a voltage that corresponds to – tracks – that input.
  • Eurorack
    Eurorack is arguably the most popular format of modular synthesizer today, with over 100 manufacturers and over 1000 modules available. It was created by Doepfer Musikelektronik in 1995, basing its size off the Eurorack format for lab equipment. Some users will try to tell you that Eurorack doesn’t “sound” as good as other formats, but that’s just based on a few substandard manufacturers or modules; there’s nothing inherent to the standard that makes a huge difference in the final sound (no; the difference between 12 and 15 volt power supplies is not enough to most ears).
  • Exponential
    In general terms, this is a mathematical curve that starts out relatively flat and then bends to climb steeply. In synthesizer terms, it most often refers to the control voltage scheme where a change of 1 volt corresponds to an increased pitch of one octave, which is doubling in cycles (vibrations) per second. This is in contrast to a linear system where 1 volt increase would always result in the same increase of cycles per second. Click through for more details.
  • Fader
    A control that can reduce the strength of a signal or voltage going through it.
  • Filter
    A module that reduced or removes certain frequencies and harmonics from the sound that is passed through it. In a synthesizer, the most typical filter types are low pass (passes all of the harmonics below its cutoff or corner frequency untouched, and then reduces the level of higher harmonics the further you go above that cutoff frequency), high pass (passes all harmonics above its cutoff frequency untouched, and reduces the level of progressively lower harmonics below the cutoff), bandpass (harmonics right around the cutoff are passed intact, and then reduced more in level the further away they are above or below the cutoff frequency), and notch (harmonics right around the cutoff frequency are reduced or cut out entirely; others above or below are allowed to live). Click through for a link to a nice demo video & article.
  • Flanger
    A signal processor often identified as the one that creates a “jet taking off” whoosh. What’s going on behind the panel is that a copy of the input signal is delayed by a very small amount (longer than a chorus effect; shorter than an echo effect) and mixed in with the original. When the delay is constant, the result is a “comb filter” where certain harmonics are cancelled out as they are mixed back on top of themselves out of phase. When the delay is varied over time, you get swooshes and sweeps. The effect was originally created by playing two tape reels of the same song, starting them in time with each other, and dragging your finger on the flange of one of the tape reels to delay it.
  • Flip-Flop
    In binary logic terms, a flip-flop toggles between high and low every time it receives an input trigger (i.e. the first trigger would set the output high, the second trigger sets it low again, and so on). In clock or audio terms, it divides the speed of an input clock or square wave by 2.
  • Flying Bus
    This is a very simple type of power distribution or bus board that typically uses a ribbon cable with multiple connectors along its length to take the output of your power supply and distribute it to your individual modules. They're cheap and easy to install and use, but in a few cases might be a cause of noise being shared between modules.
  • FM
    Frequency modulation (FM for short) refers to a synthesis technique where the pitch of an oscillator is varied (modulated) very quickly – at audio rates – by another oscillator. The result is a complex side of harmonics that may either be nicely in tune our clangorous and “out of tune” with the fundamental pitch of the main oscillator. Click through for more detail plus links to technical explanations.
  • Force-Sensing Resistor
    In modular systems, an FSR (Force-Sensing or -Sensitive Resistor) usually takes the form of a circular pad that you press on to vary a parameter. It acts as a resistor that decreases in resistance the harder you press.
  • Formant
    Many instruments based on vibrating tubes – including our own vocal tract – have certain frequencies that they like to vibrate or “resonate” at. When you send a sound down these tubes, they will accentuate the frequency of that sound (or some of its harmonics) to match these resonate frequencies. Each of these resonant frequencies is known as a formant of that instrument. A common way of synthesizing vocal-like sounds is to pass an oscillator through a filter or equalizer that has several formant peaks, spaced apart in ways that mimic certain vowels.
  • FracRack
    A less-common format of modular synthesizers put forward by PAiA and Blacet Research. It stands for Fractional Rack; one unit is 1.5” wide by 5.25” (3U) high. Click through for a link to technical details on the format.
  • Fractional Rack
    A less-common format of modular synthesizers put forward by PAiA and Blacet Research. It stands for Fractional Rack; one unit is 1.5” wide by 5.25” (3U) high. Click through for a link to technical details on the format.
  • Frequency Modulation
    Frequency modulation (FM for short) refers to a synthesis technique where the pitch of an oscillator is varied (modulated) very quickly – at audio rates – by another oscillator. The result is a complex side of harmonics that may either be nicely in tune our clangorous and “out of tune” with the fundamental pitch of the main oscillator. Click through for more detail plus links to technical explanations.
  • FSR
    In modular systems, an FSR (Force-Sensing or -Sensitive Resistor) usually takes the form of a circular pad that you press on to vary a parameter. It acts as a resistor that decreases in resistance the harder you press.
  • Function Generator
    The term function generator can have two meanings in the world of synthesis. One, test equipment that generates waveforms such as sine or square waves are often called “function generators.” Two, envelope generators are sometimes referred to as “function generators.” In both cases, “function” means to execute an equation of some sort, such as creating a periodic waveform such as a sine or creating a rise & fall in response to a trigger.
  • GAS
    Many find modular synthesis addictive, succumbing to an uncontrollable urge to keep adding more modules to their systems. Modular addicts jokingly refer to this as having a case of severe GAS: Gear Acquisition Syndrome.
  • Gate
    This is one of the main signal types that are passed around inside a modular synthesizer. It jumps to high level – typically 5 volts – when a new note is supposed to start (such as when you press a key on a keyboard controller), or when a sequencer jumps to the next “stage” or note. A gate typically stays at that level for the duration of the note (i.e. while the key is being held down), and suddenly drops or “goes low” to its resting level – typically 0 volts, but sometimes –5 volts or another number – when the note ends (i.e. when the key is released). In practice, when a gate signal is sent to a typical envelope generator, the start of the gate (when it “goes high”) tells the envelope to go through its Attack and Decay stages; while the gate remains high, the envelope stays at its Sustain level, and when the gate goes low again, the envelope moves onto its Release stage.
  • Gate Detector
    A module or section of a module that looks at a varying input voltage or even an audio signal, and then sets a gate output “high” (see above) when that signal goes above a often user-settable level (often referred to as a threshold).
  • Gear Acquisition Syndrome
    Many find modular synthesis addictive, succumbing to an uncontrollable urge to keep adding more modules to their systems. Modular addicts jokingly refer to this as having a case of severe GAS: Gear Acquisition Syndrome.
  • Glide
    Refers to a note that glides from one pitch to another while it is still audible. The music term for this effect is portamento, which is a slurring between notes. In a synthesizer, this effect is created by causing the control voltage for the pitch of a note to slide from the pitch of the previous note rather than make a discrete jump. The module that creates this effect is sometimes known as a slew generator, slew limiter, slope generator, or lag. Some use the terms glide, glissando, and portamento interchangeably, but if you want to split musical hairs, a glissando (gliss) is a different effect where the intermediate notes are more distinct – such as played rapidly in order – rather than slurred through.
  • Granular Synthesis
    Granular synthesis can be thought of as particle theory applied to sound. The concept is that a sound can be broken down into very small “grains” – typically 1-50 or 100 msec in duration. These tiny snippets are then played back to reproduce the original sound, or to create new sounds by changing the speed, pitch, volume, playback order, and direction of the individual grains. You can crossfade between these modified grains, or layer more grains on top. The result can range from audio processing tricks such as changing speed without changing pitch and vice versa, to creating psychedelic “clouds” of sound (and indeed, there is a popular module called Clouds). Click through for links to a few articles on implementing granular synthesis.
  • Hard Sync
    This is the most common type of oscillator sync where the slave oscillator will reset its waveform whenever it receives a sync pulse. If the type of sync is not specified, then it’s probably hard sync. For more details, see the entry for Sync and look at the section on oscillators.
  • Hertz/Volt
    A system where a change of 1 volt at the input results in a change in pitch of a fixed number of hertz (cycles per second), rather than a fixed musical interval. Click for more detail.
  • High (gate)
    When a gate signal is at the voltage level (typically 5 volts, although it can be more) that indicates it is “on” – such as when a note is being held down on a keyboard controller – it is said that the gate is high. (Admit it: Some of you were expecting a drug joke.)
  • High Pass Filter
    The high pass filter (HPF) design passes harmonics above its cutoff or corner frequency untouched, and reduces the level of lower harmonics depending on how far below the cutoff they are. In a 12dB/oct (decibel/octave) high pass filter, harmonics one octave below the cutoff frequency (in other words, one half the cutoff frequency) are reduced in level by 12 dB; harmonics two octaves below the cutoff (one quarter the frequency) are reduced by 24dB, and so forth. High pass filters are typically used to create bright sounds where the higher harmonics are much stronger than the fundamental and lower harmonics – for example, the sound of a harpsichord.
  • Horizontal Pitch
    HP = Horizontal Pitch. In the Eurorack format for synthesizer modules, the width of a module is defined as the number of hp (horizontal pitch) units. Each hp is 0.2”. Most modules are even numbers of hp wide, although some are odd numbers. Also, modules tend to be ever so slightly less than exactly some multiple of 0.2” wide, just to make sure you don’t run into problems with ever so slightly too wide modules overlapping.
  • HP
    HP = Horizontal Pitch. In the Eurorack format for synthesizer modules, the width of a module is defined as the number of hp (horizontal pitch) units. Each hp is 0.2”. Most modules are even numbers of hp wide, although some are odd numbers. Also, modules tend to be ever so slightly less than exactly some multiple of 0.2” wide, just to make sure you don’t run into problems with ever so slightly too wide modules overlapping.
  • HPF
    The high pass filter (HPF) design passes harmonics above its cutoff or corner frequency untouched, and reduces the level of lower harmonics depending on how far below the cutoff they are. In a 12dB/oct (decibel/octave) high pass filter, harmonics one octave below the cutoff frequency (in other words, one half the cutoff frequency) are reduced in level by 12 dB; harmonics two octaves below the cutoff (one quarter the frequency) are reduced by 24dB, and so forth. High pass filters are typically used to create bright sounds where the higher harmonics are much stronger than the fundamental and lower harmonics – for example, the sound of a harpsichord.
  • Hybrid Power Supply
    A hybrid power supply uses a lower weight, more efficient switching power supply to perform most of the drop in voltage – say, from 120v AC to 15v DC – and then uses a linear power supply for the remaining much smaller drop, such as from 15v to 12v. These are becoming the preferred design in many modular synthesizer enclosures. Shortcomings with the power supply – too noisy, or not enough – tend to be at the cause of many unexpected problems in modular synthesizers.
  • Hz/V
    A system where a change of 1 volt at the input results in a change in pitch of a fixed number of hertz (cycles per second), rather than a fixed musical interval. Click for more detail.
  • IADSR
    This is an Attack/Decay/Sustain/Release (ADSR) envelope generator that allows you to start the attack phase at an initial level – the “I” – rather than the customary 0 volts. The envelopes in the Prophet VS, as well as a module from Ladik, have this capability; IMHO more should adopt it.
  • Impedance
    Resistance it the measure we use in DC circuits; impedance is used to measure AC circuits as this value can change with frequency. Synth modules usually have their inputs and outputs defined as impedance. In general, you want a low output impedance and a high input impedance. The greater the difference between the two, the less chance the input is going to affect what’s being delivered by the output. Eurorack modules tend to have an input impedance of 100k (100,000 ohms); output impedances can vary from near zero to 1k.
  • Initial/Attack/Decay/Sustain/Release
    This is an Attack/Decay/Sustain/Release (ADSR) envelope generator that allows you to start the attack phase at an initial level – the “I” – rather than the customary 0 volts. The envelopes in the Prophet VS, as well as a module from Ladik, have this capability; IMHO more should adopt it.
  • Integrator
    This function smoothens out an incoming signal so that the change in voltage level. “Integrator” is the technical name for this math function; you are more likely to see this module called a slew limiter (where I go into more detail on its uses) or less often as a lag generator or processor.
  • Inverter
    An inverter multiplies an incoming control voltage by –1. In the case of a gate or logic inverter, it reverses the high and low states so that (for example) 0v becomes 5v and 5v becomes 0v. A control voltage inverter is often combined with an offset voltage to adjust the output voltage into the desired range. For example, if you had an envelope generator that had an output range of 0 to +8 volts, and you just inverted it, the result would be 0 to –8 volts. Since some modules such as voltage controlled amplifiers usually expect only positive voltages, you would then need to add 8 volts to that result to get an upside-down (inverted) envelope that still had an overall range of 0 to +8v.
  • Inverting Mixer
    Most signal mixers make an effort to keep the same polarity of a signal as it passes through the mixer. However, some mixers may invert the polarity or “phase” of a signal (as it’s a simpler design); other mixers may allow you to invert a signal on purpose so that you can experiment with tricks like adding one waveform or filter mode output out of phase with another coming from the same oscillator or filter.
  • IV Cable
    You often need to send one signal to multiple destinations. Options for doing this include using dedicated multiples, free-floating widgets with multiple jacks wired together, or fancy cables that allow you plug one or two extra cables into them. The IV cable is one the latter: Made by Erthenvar, it has an extra 3.5mm jack molded into the mid-point of the cable (loosely resembling an intravenous or “IV” drip), in addition to having 3.5mm plugs at either end.
  • Jack
    That hole you plug your patch cables into on the face of your synthesizer modules? That’s called a jack. The size and type of jack – 3.5mm, banana, or 1/4” – often is one of the defining features of different synth module formats: 3U/Eurorack, 4U, and 5U/MU respectively. (No, a plug is not called a Jill. Actually, it’s the other way around: A plug is sometimes referred to as a male connector, and a jack is referred to as a female connector.)
  • Keyboard Tracking
    Most modular synths follow a strict relationship between voltage and pitch, such as 1 volt per octave; any deviation would cause tuning errors. Because of this sensitivity, 1v/oct and similar signals and connections are sometimes specifically distinguished as keyboard tracking rather than just “CV” (control voltage) to make it clear they are not attenuated or otherwise modified when controlling a function on a module.
  • Keytar
    A strap-on, lightweight, portable keyboard meant to allow keyboardists the same freedom (not to mention posturing opportunities) as guitarists.
  • Lag Generator
    This function smoothes out an incoming signal so that the change in voltage level cannot exceed a certain number of volts per second. This causes the result to “lag behind” changes in the input. It is sometimes called a slew limiter or technically as an integrator. Click through for some example applications.
  • LFO
    This module produces repetitive, cycling waves ranging in frequency from the low end of the audio spectrum to as slow as many seconds or even minutes per cycle. They are used to produce effects such as tremolo (when controlling the loudness of a signal), vibrato (when controlling the pitch of a signal), repetitive filter wah-wah effects, pulse width modulation to vary the waveshape of a pulse in an oscillator, and more.
  • Line Level
    Most consumer and lower-cost professional audio equipment use a signal level reference known as line level or –10dBV (decibel volts). The most common connectors are RCA (phono) or 3.5mm, although 1/4” is also used; the signal is “unbalanced” (it uses two wires: signal and ground). In the line level standard, a sine wave that varies between +/–0.447 volts is considered to be at –10dBV. By contrast, a typical oscillator signal in a modular synthesizer is +/–5 to +/–8 volts. As a result, you will need either an output module in your modular synth or one heckuva input attenuator on your mixer or recorder to plug your synth into equipment that runs at line level. Similarly, you will need to substantially boost a line level signal to get it up to modular standards to process in your modular synth.
  • Linear FM
    The short answer is: This is often the preferred input response for frequency modulating (FM’ing) an oscillator, as the result stays in tune while you change the modulator. Click through for the longer answer.
  • Linear Power Supply
    A linear power supply design takes a higher incoming voltage and reduces it to a lower voltage using components such as transformers. In very general terms, they tend to introduce less noise into the output power signal, at the cost of increased heat and weight (they're not very efficient). Many are moving to a hybrid power supply that combines a switcher with a small linear supply or regulator to get the best of both worlds.
  • Linear VCA
    A linear voltage-controlled amplifier (VCA) uses a simple mathematical relationship between control voltage input and signal level output – for example, 50% of nominal control voltage in would result in the output signal being at 50% of the level of the input signal. This, however, is not how our ears perceive loudness; a sound must be amplified by 10x in order to be perceived as twice as loud. This makes a linear VCA desirable for scaling control voltages, but perhaps less so for scaling audio signals. If you connect an envelope generator with an exponential output to a linear VCA, then you will get the desired aural result. Confusing? That’s why it’s great when an envelope generator or VCA has a switch or control to vary it between linear and exponential response. A linear mixer is similar to a linear VCA: “half” on the input level control equals the output having half the voltage swing as the input. Again, this is fine for altering control voltages, but not for mixing audio signals; in that case you want a mixer with exponential controls.
  • Linear VCO
    A linear voltage-controlled oscillator (VCO) follows the volts/hertz (v/Hz) standard; more common is the exponential volts/octave (v/oct) standard. The exception is frequency modulation (FM), where a linear control voltage input is often preferred to recreate classic style FM as it does not change the fundamental pitch of the carrier oscillator.
  • Logic
    Binary or Boolean logic is a way of combining gate signals (on or off voltages) to create new outputs. Each section of a logic module typically includes 1 to 3 inputs, with 2 being the most common. An OR function says if there is a gate on (or “high”) signal at any of the inputs (i.e. input 1 or input 2 or input 3, etc.), to output a gate on signal. An AND function says only output a gate on signal if all of the inputs see “high” gate signals (i.e. input 1 and input 2 etc. all have gate ons). Adding an “N” to the front of a function’s name says “not” this function – in other words, a NOR function would only output a high signal if all inputs were low (not input 1 nor input 2 are high). Click through for more information and a thorough reference.
  • Logic Functions
    In a modular synth, control voltages tend to be continuous in nature, while gate and trigger signals are binary: on or off; high or low. This is the same as logic signals in digital circuitry. Therefore, some make digital logic modules. A common logic function is OR: If either signal A or signal B is high (on), then output a high gate signal (on); otherwise output a low gate (off). Another is AND: If and only if signal A and signal B are both, then output a high gate (on); otherwise, output a low gate (off). These are great functions for combining beat triggers from different timing sources.
  • Looping
    Sometimes it’s useful to have a module loop or repeat its functions. For example, an envelope generator that can be set to loop becomes a low frequency oscillator: as it attacks to a maximum value and decays back to zero, it starts that attack phase again. Quite often you want a note sequencer to loop: When it reaches the last note in the sequence, it would be useful for it to then look back to or return to the first note and start over. Audio recorders with looping features are also popular for live performance.
  • Low (gate)
    Most often, this is shorthand for saying a gate or trigger signal is in its “off” condition (typically 0 or –5 volts, in contrast to a “high” or “on” signal of +5 volts). It’s also a rather intriguing, unusually synth-heavy album by David Bowie (RIP).
  • Low Frequency Oscillator
    This module produces repetitive, cycling waves ranging in frequency from the low end of the audio spectrum to as slow as many seconds or even minutes per cycle. They are used to produce effects such as tremolo (when controlling the loudness of a signal), vibrato (when controlling the pitch of a signal), repetitive filter wah-wah effects, pulse width modulation to vary the waveshape of a pulse in an oscillator, and more.
  • Low Pass Filter
    The low pass filter (LPF) design passes harmonics below its cutoff or corner frequency untouched, and reduces the level of lower harmonics depending on how far above the cutoff they are. In a 12dB/oct (decibel/octave) low pass filter, harmonics one octave above the cutoff frequency (in other words, double cutoff frequency) are reduced in level by 12 dB; harmonics two octaves above the cutoff (four times the frequency) are reduced by 24dB, and so forth. This is the most common type of filter used, as most natural sounds have stronger low harmonics and weaker high harmonics – especially as a note fades to silence. Click through for a link to a nice video that demonstrates using a low pass filter on classic waveforms.
  • Low Pass Gate
    By strict definition, a low pass gate (LPG) is a low pass filter whose cutoff frequency goes down into the subsonic range as its control voltage goes towards 0 volts, resulting in the input signal being filtered almost into silence. Some replicate this by combining a low pass filter and a voltage controlled amplifier into the same module, with both following the same control voltage. In either case, as an input envelope falls from a high level to 0 volts, the output gets duller (higher harmonics are filtered more) as it falls to silence. This mimics the way many natural sounds work. Click through for more details and examples, including a discussion of vactrols which are often used in low pass gates.
  • LPF
    The low pass filter (LPF) design passes harmonics below its cutoff or corner frequency untouched, and reduces the level of lower harmonics depending on how far above the cutoff they are. In a 12dB/oct (decibel/octave) low pass filter, harmonics one octave above the cutoff frequency (in other words, double cutoff frequency) are reduced in level by 12 dB; harmonics two octaves above the cutoff (four times the frequency) are reduced by 24dB, and so forth. This is the most common type of filter used, as most natural sounds have stronger low harmonics and weaker high harmonics – especially as a note fades to silence. Click through for a link to a nice video that demonstrates using a low pass filter on classic waveforms.
  • LPG
    By strict definition, a low pass gate (LPG) is a low pass filter whose cutoff frequency goes down into the subsonic range as its control voltage goes towards 0 volts, resulting in the input signal being filtered almost into silence. Some replicate this by combining a low pass filter and a voltage controlled amplifier into the same module, with both following the same control voltage. In either case, as an input envelope falls from a high level to 0 volts, the output gets duller (higher harmonics are filtered more) as it falls to silence. This mimics the way many natural sounds work. Click through for more details and examples, including a discussion of vactrols which are often used in low pass gates.
  • M2.5
    A common screw thread size used to mount Eurorack modules. This size is most common when using a system of loose nuts that slide along the rails that the modules are attached to.
  • M3
    A common screw thread size used to mount Eurorack modules. This size is most common when using module mounting rails that have been pre-drilled.
  • MArF
    The rare Buchla Model 248 MArF (Multiple Arbitrary Function Generator) is a cross between a sequencer and an envelope generator (both described elsewhere in this glossary) in that it typically contains 16 or 32 stages (sometimes referred to as “segments”), and a rate control to interpolate between these stages. This means very complex envelope shapes and other control voltage sequences can be created. Later on, Buchla used the term MARF to describe the multi-step envelopes in instruments such as the Buchla 400.
  • MIDI
    Short for Musical Instrument Digital Interface. MIDI is a common language to connect one synthesizer to another, and synthesizers to a computer. Although it is a digital language, it is easy to buy a MIDI to CV/Gate (control voltage and gate) converter module that handles both note events and MIDI clocks for driving sequencers and the such. The biggest thing to watch out for is what type of connector is required: the traditional 5-pin DIN, or a USB computer-style connection.
  • Mini Keys
    A number of keyboard controllers and even keyboard synths use a key size that is much smaller than a typical piano key. Mini keys is the term commonly used (sometimes derisively, although the space and cost savings can be quite significant) to refer to this hardware choice.
  • Mixer
    This module combines signals together. You may use a mixer to combine audio signals, in which case you may want one with exponential level controls and perhaps stereo panning, or to combine control voltages, in which case you may want linear level controls plus additional functions to invert and offset the voltages going through it. Click through for a link to an article on choosing utility mixers.
  • Modular
    A modular synth breaks down the main components of a synthesizer – the tone-generating oscillators, the tone-modifying filters, the amplitude-shaping VCAs, and the modulation sources that create envelopes, tremolos, and more – into individual modules you can purchase and install. At the most basic level, this allows you to play mix-and-match in building your own custom synth. Click through for more reasons to go modular.
  • Modulation
    When you vary a parameter of a synthesizer module using voltage control, it is said that you’re modulating that parameter. For example, when a low frequency oscillator (LFO) varies the cutoff frequency of a filter to create a wah-wah effect, it is said that the LFO is modulating the cutoff. When an envelope generator causes a voltage controlled amplifier (VCA) to open up to allow a sound to become suddenly loud, and then fades it back down to silence, you can also say the envelope is modulating the amp (although some like to restrict the term “modulate” to a repetitive action). Therefore, we call the sources of these changes modulators. Click through for a link to a nice introductory video on modulation.
  • Modulator
    We touched on the general subject of modulation and modulators in the definition above. However, quite often when someone uses the term modulator, they’re usually discussing a synthesis techniques where one usually audio-rate signal “modulates” (varies) another audio signal. For example, in frequency modulation (FM) synthesis, the modulator (or modulating oscillator) varies the frequency (pitch) of the main signal generator (oscillator), called the carrier. In ring, balanced, or amplitude modulation, the modulator is varying the loudness of the carrier signal. So the term modulator is a way to make it clear which component you’re talking about in one of these patches: not the main tone generator, but the module that is driving that generator crazy.
  • Monophonic
    A monophonic instrument is only capable of playing one note at a time. Common examples include brass and woodwind instruments as well as the human voice. A typical modular synthesizer voice is also monophonic, as it requires so much hardware and effort to patch together the components required to make that one note. Click through for more details.
  • Morphing
    In the context of a modular synth, morphing refers to an oscillator that can more or less smoothly change the shape of its output waveform – and therefore, the resulting sound – as you play it. This is usually the domain of digital oscillators which internally crossfade (or in some cases, switch) from one waveshape to another, although it is sometimes applied to analog oscillators that give you real time control over waveshapes.
  • Mother-32
    A very popular semi-modular synthesizer by Moog. It comes in its own case, but can be mounted in a Eurorack-format case. It comes with one VCO (sawtooth and pulse waveforms), one LFO (triangle and square waveforms), one Moog-style transistor ladder filter that can be low pass or high pass, and one AD or AR envelope generator. It also has a very capable step sequencer plus a miniature one-octave keyboard. What makes it a semi-modular is a nice patch panel that allows alternate routings for the way the synth voice is internally wired, and for it to be patched to external modules. As so many of these were sold, I’m using it as a representative of a typical semi-modular or “starter” synthesizer voice when discussing how to expand a basic modular system. I have an online introductory course to the Mother-32 coming out this spring, and will have a course plus ongoing weekly series on adding different modules to this starter system.
  • MU
    Refers to modules that are 5U (rack units) or 8.75” high, which is most often associated with the vintage Moog standard and those who have followed in their footsteps, including Synthesizers.com (Dotcom) and Moon Modular. You will sometimes hear this used interchangeably with MU for Moog Units, which also refers to a standardized width of 2.125” wide per MU. Given that this standard is both historical and physically large, some users “5U” as a badge of honor that they’re traditional and cool. (And the are.) There was also a briefly popular 5U format from MOTM that used a different width and power connection. It has since been discontinued, but there are still diehard MOTM format users today.
  • Multi-Tap Delay
    A delay works by in essence putting audio in one end of a pipe and grabbing it again when it comes out the other. A multi-tap delay says “Why wait until the audio snapshots go all the way through the pipe? Let’s grab it when it’s only part way through the pipe.” Those points where it’s prematurely grabbed are the “taps” – kind of like additional water taps added along a long pipe. Click on the name "multi-tap delay" for more details and background.
  • Multiple
    Quite often you need to split or copy a signal to send to more than one destination. This is commonly done with a multiple (“mult” for short) where you plug one source in, and then plug in additional patch cables to go off to multiple destinations. Click through for details on the different types of mults.
  • Multiple Arbitrary Function Generator
    The rare Buchla Model 248 MArF (Multiple Arbitrary Function Generator) is a cross between a sequencer and an envelope generator (both described elsewhere in this glossary) in that it typically contains 16 or 32 stages (sometimes referred to as “segments”), and a rate control to interpolate between these stages. This means very complex envelope shapes and other control voltage sequences can be created. Later on, Buchla used the term MARF to describe the multi-step envelopes in instruments such as the Buchla 400.
  • Multiplexer
    Multiplexing is a technical way to describe signal routing, where multiple signals may be routed to one destination. In synth modules, this is usually extended to include the possiblity of one input being switched between multiple outputs. A sequential switch is a type of multiplexor, as it chooses among multiple inputs to decide which one to send to the output (or the other way around). There are some modules that do this at audio rate, using an oscillator's output to switch between variations of another waveshape to create complex, chopped mixtures of those waveforms.
  • Multitimbral
    As we mentioned in the entry for monophonic, smaller modular synths may only be able to create one note at a time. Larger systems with enough modules to play multiple musical lines at once – each with a different tone or patch per line – are referred to as being multitimbral, as in being able to create multiple timbres (tones) at the same time.
  • Musical Instrument Digital Interface
    Short for Musical Instrument Digital Interface. MIDI is a common language to connect one synthesizer to another, and synthesizers to a computer. Although it is a digital language, it is easy to buy a MIDI to CV/Gate (control voltage and gate) converter module that handles both note events and MIDI clocks for driving sequencers and the such. The biggest thing to watch out for is what type of connector is required: the traditional 5-pin DIN, or a USB computer-style connection.
  • Mute
    Sometimes you need to silence or disconnect a signal. A circuit that allows you to do so is called a mute. (Disappointed that it’s not something more exotic, like a module that accurately emulates a trumpet mute? Sorry. But that’s not a bad idea…)
  • Noise
    Noise, in short, is a random signal. It is most often identified as a sound that does not have a distinct pitch, such as hissing, breath noise, or the sound of wind or the surf. It can also be a slow moving control signal that replaces a low frequency oscillator but which is random rather than periodic and predictable in nature. Noise is often described by different “colors” such as white, pink, red, or blue which have different frequency distributions. Click through for some applications of noise, plus a useful link.
  • Normalled
    The power of modular synthesizers is that you can patch a signal to flow the way you prefer through your system. This can also be a time-consuming bummer when you’re just trying to patch a “typical” signal flow. Therefore, some manufacturers have created “semi-modular” synths that have all of these typical connections pre-wired for you, with the important feature that many of these wirings can be overridden by inserting patch cables into the correct jacks. These pre-wired connections are often referred to as being normalled. For example: An internal noise source may normally be connected to one channel of a mixer that appears before the filter, but if you insert a patch cable into a jack usually labeled external input, this “normalled” connection is broken and replaced by your external connection.
  • Notch Filter
    This is a particular type of filter mode where audio frequencies or harmonics around the corner or cutoff frequency setting are removed, nor “notched out” of the overall spectrum. It is the opposite of a bandpass filter, which only passes harmonics around the cutoff frequency. Notch filters tend to have a subtle effect on the sound; moving (modulating) the cutoff frequency can result in a weak phasing sort of sound. Notch filters are often used in sound systems to weaken or remove a problematic frequency, such as ground loop hum, a resonance in a room, or other annoying peak in the harmonic spectrum of a sound. Think of using a notch filter in a patch to hollow out a sound, leaving room in the harmonic spectrum for other sounds to exist with less competition, or just to create a sound more likely to catch the ear because something that is expected is instead missing.
  • Octave
    An octave is a typical musical internal. For example, all of the “C” notes on a keyboard are octaves apart from each other. To play a note that is one octave higher in tuning, you need to double its pitch; to play an octave lower, you need to cut the pitch in half. In patch terms, this typically means adding or subtracting 1 volt to get a one octave change in pitch; some oscillators also have octave switches on their front panels that add or subtract these voltages for you (all they are not always perfectly accurate; you often need to re-tune after switching octaves). Suboctave or subharmonic generators divide the input pitch by 2 or 4 to create new waveforms that are one or two octaves lower in pitch, which adds bass.
  • Octave Divider
    A module that creates a new tone one or two octaves below the fundamental harmonic – the “pitch” – of the sound coming into it, to emphasize the bass. Sometimes also known as a suboctave or sub bass function.
  • Offset
    In simple terms, Offset modules usually add or subtract a voltage from a signal passing through - such as shifting a 0 to +10v signal to instead vary between -5 and +5 volts. For examples why that would be useful, click through.
  • Operational Transconductance Amplifier
    An OTA (operational transconductance amplifier) circuit is one that converts an input voltage to an output current. This is a popular amplifier design as it can be less prone to going into saturation (clipping), has good bandwidth, and is also known for a “warm” sound. Therefore, you may find it in VCAs (voltage controlled amplifiers). Current can be thought of as the inverse of resistance, so what you have in an OTA circuit is in essence a voltage to resistance device that makes it possible to add voltage control to circuits such as filters. In general, when someone touts they have an OTA based filter, they usually mean it has a “warm” sound...unless it’s an MS-20 filter clone, in which case it’s thinner and more edgy. In reality, using an OTA is more about convenience of design than creating a specific sound. Click through for a few more details.
  • Operator
    There are a few different synthesis techniques where one usually audio-rate signal does something to another audio signal. For example, in frequency modulation (FM), a second signal (called the modulator) varies the frequency (pitch) of the main signal, called the carrier. These two signals or oscillators are often referred to as operators, particularly in FM patches. You’re more likely to hear this term used when working with a dedicated FM synthesizer like a Yamaha DX-7 and its descendants, than with a modular system.
  • OR function
    One of the most common Boolean or binary logic functions, OR says if there is a gate on (or “high”) signal at any of the inputs (i.e. input 1 or input 2 or input 3, etc.), to output a gate on signal. A NOR function has an inverted output: it would only be on (high) if all inputs were low (not input 1 nor input 2 are high). An XOR (Exclusive OR) would only output a high signal if one of the inputs was high, but not if both inputs were high (or low). Finally, an XNOR is the invert of an XOR function.
  • Oscillator
    At its core, to oscillate means to vary back and forth in a repeating pattern. The main sound generator in a modular system is called an oscillator because its output varies up and down (oscillates) in voltage in a repeating pattern. This pattern is referred to as its waveshape (such as a square wave, that alternates between high and low voltages); how fast this pattern repeats is called its frequency or pitch. An acoustic instrument equivalent of an oscillator is a string that vibrates back and forth on a guitar, a drum head that vibrates up and down, or the vibrations in the reed of a woodwind instrument. The vibrations of a modular synth’s oscillator just happen with electricity going down a wire rather than a physical object vibrating in air. (Eventually this electricity is routed to a speaker, which then vibrates the air with the same pattern sent to it over a wire.)
  • OTA
    An OTA (operational transconductance amplifier) circuit is one that converts an input voltage to an output current. This is a popular amplifier design as it can be less prone to going into saturation (clipping), has good bandwidth, and is also known for a “warm” sound. Therefore, you may find it in VCAs (voltage controlled amplifiers). Current can be thought of as the inverse of resistance, so what you have in an OTA circuit is in essence a voltage to resistance device that makes it possible to add voltage control to circuits such as filters. In general, when someone touts they have an OTA based filter, they usually mean it has a “warm” sound...unless it’s an MS-20 filter clone, in which case it’s thinner and more edgy. In reality, using an OTA is more about convenience of design than creating a specific sound. Click through for a few more details.
  • Parameter
    Parameter is the fancy name given to any value or property or control of a synthesizer module that you’re trying to change. For example, an oscillator’s parameters typically include its pitch and the width of its pulse wave. A filter’s parameter will include its cutoff frequency (pitch), the amount of resonance (feedback), and possibly other controls such as a blend between its different outputs. Parameter was a popular term to describe a value you could change in software, and it’s been carried over by some to hardware modular synths.
  • Paraphonic
    A paraphonic synth is one where all of the notes being played go through a single filter (VCF) and amplifier (VCA). This was a popular scheme in the early days of polyphonic synths in that a separate oscillator (or organ-like frequency divider, in the case of “string synths” and the such) was used for each note played, but they were mixed before all going to the filter and amp to articulate the note(s). It was not uncommon for some monophonic synths to allow two to four independent notes to independently control the pitch of its oscillators, while still going through a single filter. This works great for chords; it doesn’t always work all that great for when a new note is played while others are being held as all of the notes will be re-articulated together. Click through for a link to an article that explains the differences between multi, poly, and paraphonic.
  • Passive
    Means no active (i.e. connected to a power supply) electronics are involved – such as sending a signal straight through a potentiometer control, instead of using op amps and other electronics to create a mixer circuit around it. Passive is cheap and easy, and does not add noise to a signal. But passive electronics cannot buffer one signal from another (meaning they might interact in undesirable ways), and cannot boost, offset, or invert a signal.
  • Patch
    The shorthand term used to refer how a series of modules are interconnected to create a sound, derived from the fact that patch cords are used to connect the modules together.
  • Patch Cable
    The cables used to connect together the different inputs and outputs in a modular synthesizer, carrying electrical control voltages and audio. The term came from the old telephone patch boards where an operator had to physically connect two callers together using electrical cables. As different modular formats often use different connector standards, you need to make sure the connectors at the ends of the wire in a patch cord are the size you need (3.5mm for Eurorack, 1/4” for 5U/Moog Unit, or banana for Serge or Buchla control voltages).
  • PD
    Phase Distortion synthesis was used by Casio originally in the 80s in the CZ line of synths. It is related to FM (frequency modulation), with enough differences to avoid problems with the patent used by Yamaha’s FM synths of the era. Intriguingly, it did a good job at mimicking many “analog” synth effects including the sound of a resonant filter. Click through for the technical details.
  • Phase
    One cycle of a waveform is considered to have 360 degrees, just like a circle. How far you move around the circle (or through the waveform) can be defined by the phase. For example, if you are one-quarter of the way through a waveform’s cycle, your phase is 90°. Click through for more.
  • Phase Distortion Synthesis
    Phase Distortion synthesis was used by Casio originally in the 80s in the CZ line of synths. It is related to FM (frequency modulation), with enough differences to avoid problems with the patent used by Yamaha’s FM synths of the era. Intriguingly, it did a good job at mimicking many “analog” synth effects including the sound of a resonant filter. Click through for the technical details.
  • Phase Locked Loop
    A phase locked loop is, in essence, an oscillator that tries to match the frequency of – or more importantly, a division or multiple of the frequency of – another signal. This is most commonly used to create a frequency that is much higher than the incoming reference signal – such as a timing module that can create an output clock that is 2, 4, 8, or more times the tempo of an incoming clock, or a very high frequency oscillator that is locked to a multiple of an incoming pitch – perhaps to drive a special circuit such as a switched-capacitor filter. Click through for more detail and a few technical links.
  • Phase Modulation
    Some would say this is the pedantically correct term for frequency modulation (FM), as the act of causing a carrier oscillator to play back faster and slower (quickly changing its frequency to be higher and lower) is the same as advancing and retarding position (phase) of the normal playback of a waveform. But don’t get bogged down by terminology when creating an FM patch; just connect the output of one oscillator to the pitch input of another and go for it.
  • Phase Shifter
    This effect splits a signal into two copies. One copy is fed through an “all pass filter” which does not attenuate any of the original harmonics like a low pass or high pass filter does, but which does alter the phase of the signal, causing those harmonics to have varying amounts of phase shift in relation to the original depending on their frequency. Mix these two copies back together, and different harmonic components of the original sound cancel each other out (see Phase), resulting in a notch filter effect. Each “stage” – all-pass filter section – of a phase shifter creates one of these notches. More stages create more notches, and a deeper effect.
  • Physical Modeling
    One approach to (often digital) synthesis is to recreate the components of actual instruments – such as a vibrating string or tube, or a resonating body such as the shell of a guitar or drum – and string those together to create sounds. There are a handful of modules available which perform this modeling to create their sounds.
  • Pink Noise
    Noise is a random, unpitched signal that, at audio rates, can sound like hissing or the wind. Pink noise has equal energy (sound level) per octave. As each higher octave has double the frequency of the octave below it which spreads out the energy over a wider range of frequencies, pink noise tends have a more natural, less electronic sound with more bass and less high end – especially when compared to white noise, which has an equal energy per number of hertz (frequency) and therefore tends to sound very bright. Click through for a link to graphs and audio examples for the different colors of noise.
  • Pitch to Voltage Converter
    PVC stands for pitch to voltage conversion. In the quest to play a voltage-controlled synthesizer with something other than a keyboard-like thingy (touch plates included), some have designed modules or other equipment that attempt to detect the pitch of an audio signal – say, from a guitar, flute, or singer – and convert that pitch to a corresponding voltage that can drive a VCO in unison with the original sound. That's the good news; click through for the bad news.
  • PLL
    A phase locked loop is, in essence, an oscillator that tries to match the frequency of – or more importantly, a division or multiple of the frequency of – another signal. This is most commonly used to create a frequency that is much higher than the incoming reference signal – such as a timing module that can create an output clock that is 2, 4, 8, or more times the tempo of an incoming clock, or a very high frequency oscillator that is locked to a multiple of an incoming pitch – perhaps to drive a special circuit such as a switched-capacitor filter. Click through for more detail and a few technical links.
  • Pole
    This is a technical term that helps describe the design of a filter. Each pole of a filter attenuates frequencies beyond its cutoff or corner frequency by 6 decibels (dB)/octave; the more poles, the stronger the filtering effect. A 4-pole low pass filter, for example, attenuates frequencies one octave above its cutoff frequency by 24 dB; frequencies two octaves above the cutoff are attenuated by 48 dB and so forth.
  • Polyphonic
    The term "polyphonic" refers to a synthesizer that can play more than one individually articulated note at a time; in most cases, those notes all play a similar sound or patch. Click through for more details on how this is implemented, and the results.
  • Portamento
    This refers to a note that glides from one pitch to another while it is still audible – in other words, a slurring or sliding between notes. In a synthesizer, this effect is created by causing the control voltage for the pitch of a note to slide from the pitch of the previous note rather than make a discrete jump. The module that creates this effect is sometimes known as a slew generator, slew limiter, slope generator, or lag. Some use the terms glide, glissando, and portamento interchangeably, but if you want to split musical hairs, a glissando (gliss) is a different effect where the intermediate notes are more distinct (including being played individually) rather than slurred through.
  • Power Distribution Board
    This simple circuit board takes the output of your modular system's power supply and creates multiple copies of it, routed to connectors that go to your individual modules. Click through for advice on finding the best bus board designs, and how to connect them.
  • PPQN
    When you send a clock signal (usually a gate signal or other electrical pulse) around a modular synth to move sequencers through their steps and the such, it’s good to know how fast that clock is pulsing. This is usually defined in terms of how many pulses there are per quarter note – PPQ or PPQN for short. If the clock is just happening every quarter note, then the clock speed is 1 PPQN; in the case of DIN Sync (a popular standard among early Roland synths, with DIN being the type of electrical connector used) or MIDI clocks, the standard is 24 PPQN. This means the master pulse can define a triplet for every 8th note (8 x 3).
  • Precision Adder
    Synthesizers are very sensitive to unintentional variations in pitch control voltage – any error can result in the oscillators under control going out of tune. Therefore, whenever you add together pitch control voltages inside a modular synth, you really should be using a precision adder that precisely adds together the pitch voltages without introducing an error. Ordinary mixers might slightly attenuate or amplify a voltage passed through them, which in most cases would create tuning errors. Click for a link to an article where I explain why you should have one in your system.
  • Preset
    We’re talking modular synths here – there are no presets. You have to patch every sound yourself. (Okay – some digital modules with lots of parameters allow you to recall or even store presets of common settings. But that doesn’t count.)
  • Pressure
    Some keyboards measure how hard you press down on the keys, and convert this to a voltage (or other control signal such as MIDI, which can then be converted into a control voltage) that you can use to add expression to a note, such as adding vibrato or opening the filter wider. Monophonic aftertouch measures one pressure value for the entire keyboard, regardless of which key(s) you are pressing; polyphonic aftertouch produces a signal for each individual key. Important trivia: Touch plate keyboards actually measure the surface area of the skin touching them rather than pressure or force – so you can increase or decrease the aftertouch amount by rolling between the tip and length of your finger.
  • Pulse
    Pulse has a couple of different meanings in a modular synth. When you alter the shape of a square wave so that one portion is narrower than the other, it is referred to a pulse wave (see Pulse Wave Modulation below). Also, a narrow gate or trigger used as a clocking signal for sequencers and the such is often referred to as a pulse.
  • Pulse Per Quarter Note
    When you send a clock signal (usually a gate signal or other electrical pulse) around a modular synth to move sequencers through their steps and the such, it’s good to know how fast that clock is pulsing. This is usually defined in terms of how many pulses there are per quarter note – PPQ or PPQN for short. If the clock is just happening every quarter note, then the clock speed is 1 PPQN; in the case of DIN Sync (a popular standard among early Roland synths, with DIN being the type of electrical connector used) or MIDI clocks, the standard is 24 PPQN. This means the master pulse can define a triplet for every 8th note (8 x 3).
  • Pulse Width Modulation
    Most oscillators that output a square waveform also have an additional control voltage input that sets the width of the top portion of the “square” wave (obviously, making the top portion wider makes the bottom portion narrower and vice versa). The act of varying the width of the resulting pulse wave creates a sort of Doppler shift; varying the width back and forth – for example, by modulating the pulse width with a low frequency oscillator – creates a chorusing effect that can sound like a detuned pair of oscillators. The resulting effect is referred to as pulse width modulation.
  • PVC
    PVC stands for pitch to voltage conversion. In the quest to play a voltage-controlled synthesizer with something other than a keyboard-like thingy (touch plates included), some have designed modules or other equipment that attempt to detect the pitch of an audio signal – say, from a guitar, flute, or singer – and convert that pitch to a corresponding voltage that can drive a VCO in unison with the original sound. That's the good news; click through for the bad news.
  • PWM
    Most oscillators that output a square waveform also have an additional control voltage input that sets the width of the top portion of the “square” wave (obviously, making the top portion wider makes the bottom portion narrower and vice versa). The act of varying the width of the resulting pulse wave creates a sort of Doppler shift; varying the width back and forth – for example, by modulating the pulse width with a low frequency oscillator – creates a chorusing effect that can sound like a detuned pair of oscillators. The resulting effect is referred to as pulse width modulation.
  • Q
    If you come from the pro audio world, you may be used to Q referring to the width or narrowness of a peak or notch filter. In a synthesizer filter, when you increase the resonance (feedback), a peak forms around the cutoff frequency of the filter’s curve or shape. The higher the resonance, the higher and narrower this peak. As a result, some used to use the audio term Q to refer to the resonance amount, although you don’t hear that term used nearly as much today.
  • Quadrature
    You can define a full cycle of a waveform as consisting of 360 degrees, akin to a circle. One quarter of the way around this circle – or moving to a point that is one quarter of the way through a cyclical wave – is 90°. A sine and cosine wave are shifted 90° degrees or a quarter cycle out of alignment (phase) with each other. Since this is a quarter of a cycle, this is often referred to as a quadrature relationship. Click through for some applications of this.
  • Quantizer
    A quantizer auto-corrects the input voltage to the nearest desired target, such as the voltage that corresponds to a semitone or other note in a scale. These are occasionally built into modules like sequencers or oscillators, but quite often they are standalone modules. Click through for more details.
  • Rack Rash
    When you mount a module into a case, the head of the screw or bolt used to mount the module can scratch the faceplate of the module. These scratches are referred to as rack rash. You can almost never see it when you mount a module, as the scratches are behind the screw or bolt head, but nonetheless some will pay more for a used module that is unscratched. So buy a bag of plastic washers and put them behind the screw or bolt head just to remove another reason for someone to not buy your used module.
  • Rack Unit
    Rack-mounted equipment usually follows a standard set of dimensions, including 19” for width, and a “rack unit” (or U for short) for height equaling 1.75” per U. Many common modular synthesizer formats follow the rack unit system for standardizing module height – such as 3U (3 x 1.75 = 5.25”) for Eurorack, 4U for Buchla and Serge, and 5U for classic modular Moogs (sometimes referred to as MU for Moog Unit).
  • Ramp
    In general, a ramp refers to any voltage that is steadily raising or falling; quite often it resets when it reaches a target voltage and starts over again. A sawtooth oscillator waveform is sometime referred to as a ramp. Sometimes, the individual stages of an envelope generator are also referred to a ramp as it raises from 0 volts to a maximum level such as 5v for the attack stage, then falls from this peak to the sustain level for the decay stage.
  • Random
    Most voltages moving around inside a modular synth are very purposeful in their variations: the repeating waveforms of an audio rate or low frequency oscillator; the rising then falling voltages of an envelope generator. However, it can also be useful to have randomly wandering voltages to create everything from subtle variations in pitch to wildly varying volumes or filterings. Noise is an example of an audio-rate random signal.
  • Ratcheting
    This is a trick used with sequencers where one stage of the sequence may be triggered quickly multiple times, rather than just once as you step to that stage. For example, the result may be a series of quarter notes, with a burst of four sixteenth notes appearing instead for one or more stages. Click through for some patch ideas on how to accomplish this.
  • Rate
    This word is used sometimes to refer to the speed or frequency of a low frequency oscillator or similar repetitive function, such a sequencer’s tempo clock.
  • Recapping
    Electronic components can age. Certain types of capacitors – namely, electrolytic and tantalum, often used in the power supply section – are the most likely to deteriorate over time; some put the maximum safe life of an electrolytic capacitor to be 25 years. Therefore, serious vintage synth owners “recap” (replace the age-sensitive capacitors in) their older equipment.
  • Red Noise
    Also referred to as brown noise, technically it’s a type of noise whose power density (spectral loudness) decreases 6 dB per octave with increasing frequency. It has a bass-heavy sound, akin to the sound of the surf at a distance. It can also be used a slowly changing random control voltage or modulation signal, instead of as an audio source.
  • Regeneration
    Regeneration can have a couple of different meanings inside a synth, both meaning feedback. An echo unit can feed some of its output back into its input, causing the delayed signal to be repeated again; this is sometimes referred to as regeneration. Also, very rarely you will hear resonance in a filter referred to as regeneration.
  • Release
    This refers to the final stage of an envelope that typically falls back to zero volts, usually resulting in silence. It is often used in the context of talking about an Attack/Release (AR) or Attack/Decay/Sustain/Release (ADSR) envelope generator, but can refer to any final stage of an envelope.
  • Reset
    The Reset input on a module accepts a trigger or gate signal, and tells the module to go back the beginning of whatever it was doing. In the case of a clock divider, this means pretend the next clock is the first clock you should be counting in the division (more on that in the full definition). In the case of a sequencer, it means go back to the first stage. In the case of an envelope, it means go back to the start of the attack. In the case of a gate delay, it means to re-start the timer for the delay.
  • Resonance
    When the output of a filter is fed back into its input, the result is an increased boost in the harmonics right around the filter’s cutoff or corner frequency. The audible result is similar to playing a sound in a room that has a resonance – sympathetic, reinforcing echo or vibration – at a certain frequency. Therefore, the term resonance is often used to refer to a filter’s feedback amount.
  • Resonator
    Many acoustic instruments include a body or sound chamber that “resonates” – sympathetically vibrates at, or reinforces – one or more frequencies. To simulate this effect in modular synths, you can get a specialized filter or equalization module that boosts the sound at typically three or so user-definable frequencies, each usually within a narrow band. This is one of the secrets of synthesizing real-world sounds or spaces.
  • Reverb
    Short for reverberation. This is an effect device that mimics being in a room where you can hear the original sound reflect off the walls multiple times, bouncing around in a wash of sound until it eventually decays into silence. A reverb can greatly enhance the sound of a synthesizer, adding lushness and dimension to what might otherwise be a stark sound. There are relatively few modules that implement a reverb effect, and even fewer that allow you to voltage control some of its parameters (the ErbeVerb being the most famous); many just use an external reverb effect.
  • Ribbon Controller
    This is a long strip that is capable of measuring the position where you press it along its length, and the pressure used to press it. It can be used as an alternate keyboard or as a pitch bend controller, with the position determining pitch. Shorter versions also appeared sometimes as alternate controllers on synthesizers, such as the Yamaha CS-80. Click for more details including links to both old and modern ribbon controllers.
  • Ring Modulator
    Balanced or ring modulation is a special type of amplitude modulation, where one bipolar (swinging both above and below 0 volts) signal – the modulator – is used to vary the amplitude of a second bipolar signal, known as the carrier. The modulator’s frequency is both added to and subtracted from the carrier’s frequency; the resulting harmonics replace the original carrier and modulator. Click for more details.
  • S-trig
    Some systems – such as the original Moog modular – use an s-trigger (switch or shorting trigger) instead of a normal gate, which was a wire that was shorted to 0 volts ground, like the closing of a switch wired to ground. You cannot interconnect these two systems without some form of conversion between the two, which can be as simple as a special cable.
  • S/H
    A sample and hold (S/H) module has two inputs: a signal that is being sampled, and a trigger input that indicates when the first input should be sampled. When a trigger is received, the current voltage at the first input is sampled (measured) and held (stored), and presented at the output. This stable voltage is held until a new trigger is received. Sample and holds are most often associated with creating stepped random voltages. To do this, noise is fed to the main input; whenever a trigger is received, the voltage present at that input is some random value, which is then dutifully sent to the output.
  • Sallen-Key
    The Sallen-Key filter topology or design creates a "second order" or two-pole low, high, or bandpass filter and is capable of high resonance or Q. This is the design used in the Korg MS-20 filter and its clones, among others. Click through for more details + links.
  • Sample & Hold
    A sample and hold (S/H) module has two inputs: a signal that is being sampled, and a trigger input that indicates when the first input should be sampled. When a trigger is received, the current voltage at the first input is sampled (measured) and held (stored), and presented at the output. This stable voltage is held until a new trigger is received. Sample and holds are most often associated with creating stepped random voltages. To do this, noise is fed to the main input; whenever a trigger is received, the voltage present at that input is some random value, which is then dutifully sent to the output.
  • Sample Rate
    This is a specification of digital audio: How fast the individual measurements (samples) that reconstruct a sound are recorded or played back. The bandwidth of that audio file (which corresponds to the highest frequency that can be reproduced) is in practice a bit less than half of the sample rate. Click through for some details on the implications of this.
  • Saturation
    On a simple level, saturation is a fancy word for clipping: Once the input voltage goes higher (or lower) than a circuit can handle, it is instead held at that limit. However, saturation usually implies a more rounded, shaped approach to that clipping limit, resulting in a more pleasing (or at least less annoying) form of distortion. Tubes circuits are often associated with this soft clipping behavior, although it can be emulated in other circuits or even digital signal processing. Different devices may be sought out for specific sonic character of the way they.
  • Sawtooth
    One of the most common waveforms produced in a synthesizer. This ramp-shaped wave contains both even and odd harmonics, strongest at the fundamental frequency (the note being played) and diminishing at the higher frequencies. The result is very bright, loud, “brassy” sound.
  • Schmitt Trigger
    This is a type of gate detector that looks at a varying input signal and outputs either a “high” (typically 0, 10, or even 15 volts) signal or a “low” signal (typically 0 volts). When the input goes above one reference threshold – say, 4 volts – the output goes high. When the input then goes back below a second, different threshold – say, 1 volt – then the output goes back low. Click through for some applications of this.
  • SEM
    The Oberheim SEM (Synthesizer Expander Module) was one of their earliest products. It was an entire synthesizer voice – two oscillators, two simple envelopes, VCA, and a very popular two-pole state variable filter design with a knob that crossfaded between low pass, notch, and high pass outputs plus a separate bandpass setting – in a cube-like case. Most often today, when a modular manufacturer uses the magic letters "SEM", they're referring to a filter meant to emulate that in the original Oberheim synth. Click through for a little more history, as well as a link to Tom Oberheim's current company which is still producing SEM-derived synths.
  • Semi-modular
    The components of a semi-modular synth – such as the oscillator, filter and amplifier – are pre-wired behind the front panel in what the manufacturer considers to be a typical, logical way. However, they also provide patch points either to access some of its functions (such as the individual waveform outputs of the oscillator) to send to other modules, or to override that pre-wiring. Many who are new to modular synthesis dip their toe in the water by getting a semi-modular synth, and then expanding it with additional modules. Click through for a link to an article I wrote about semi-modular vs. modular synths.
  • Semitone
    Also known as a half step or half tone, this is the smallest pitch division in most Western music – such as the difference between a C and a C#. With equal temperament (the most common way of tuning a Western scale), this pitch division is 1/12 of an octave.
  • Sequencer
    The most common type of sequencer you’re going to see in a modular synth contains a row of knobs (also known as steps or stages) that may each be set to output a different voltage. A sequencer then goes through steps one at a time. This is most often used to create repetitive musical lines where each note has the same duration, which is popular in trance-like forms of music as well as the classic Berlin School style (70s-era Tangerine Dream and Klaus Schulze; current Red Shift and Node). Click through for features to be aware of in a sequencer.
  • Sequential Switch
    This module comes in a few different forms; in the most common, a few different inputs are routed to one output (although they are usually symmetrical – one input can be switched between several outputs). A pulse or gate input then steps through the inputs one at a time, switching which ones is routed to the output. Fancier sequential switches allow you to set the number of stages, to divide an input clock so it switches at a slower tempo than the master clock, or might directly route a series of inputs to corresponding outputs (with usually a summed output as well).
  • Sine
    This is the purest waveform: It contains only the fundamental harmonic, and no higher harmonics. As a result, it’s a great wave to use to create a sub bass as well as a kick drum or other pure drum tone; it’s also a great source wave to use when exploring techniques such as frequency modulation (FM), amplitude modulation (AM), or wavefolding which add or shift harmonic content.
  • Slew Limiter
    This function smoothes out an incoming signal so that the change in voltage level cannot exceed a certain number of volts per second. As a result, it is sometimes called a lag generator or processor, or more technically as an integrator. Click through for some application ideas.
  • Sliding Rails
    This is a common system for mounting modules into a case where the rails that the modules attach to contain channels rather than holes. A number of nuts are inserted into these channels, which can then be slid to any position to accommodate the mounting hole spacing of your modules. In a Eurorack case, these nuts tend to have a 2.5mm or 3mm hole and corresponding thread. Click through if you're curious about the pros and cons of this approach.
  • Slope
    Most filters typically have a cutoff or corner frequency they are tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that it harmonics get progressively quieter the further away they are from this cutoff. The strength of this effect is referred to as its slope. Most filters have slopes that are defined multiples of 6 decibels (dB) weaker for each octave further away you get from the cutoff frequency. For example, a low-pass filter (LPF) with a slope of 24 dB/octave would attenuate harmonics one octave above its cutoff frequency by 24 decibels.
  • Slope Generator
    A slope generator creates ramps: rising or falling voltages. It is essentially a gate generator and a slew limiter (see above) wired together in the same module. A common example of a slope generator is an attack/decay (AD) or attack/release (AR) envelope generator. However, since it can be used for generalized control voltage functions – even creating a sawtooth or triangle wave oscillator – some companies such as Buchla and Serge referred to by its elemental function of generating sloping voltage changes.
  • Sound Modeling
    A technique that recreates a sound without directly modeling the physical device. An example is additive synthesis, which uses a combination of sine waves and noise to recreate sounds.
  • Splitter
    The short definition is something that can divide a signal into two or more copies, such as a splitter cable where two outputs are wired to one input. For a deeper discussion, see the entry on multiple, as there are ways of going about this beyond simple wiring.
  • Square wave
    This is a common waveform produced by a synthesizer’s oscillator. It alternates between a high and low voltage (typically +/-5 or 8 volts for an audio oscillator; sometimes low frequency oscillators go between 0v and a positive voltage). Aside from being a really easy waveshape to generate with analog circuitry, it has an interesting harmonic series: it has a strong fundamental, then gradually weaker odd harmonics: a component at three times the fundamental frequency, one at fives time the fundamental, and so forth. The result is a more open, hollow sound, especially when compared to a sawtooth (ramp) wave that has both odd and even harmonics present. Click through for details about its cousin, the pulse wave.
  • Stackable Cable
    Many banana style cables are constructed that each plug has a jack built into its back, allowing you to plug another cable directly in top of the original plug. These are used by Buchla and Serge-compatible systems. TipTop makes a similar cable using 3.5mm plugs and jacks for Eurorack format users called Stackables. Click through for some useful links.
  • Stage
    In the most general terms, a stage is the next change in voltage among a series of changes. In an 8-step sequencer, for example, each new note that it produces in order is a stage. In an envelope generator such as an ADSR (Attack/Decay/Sustain/Release), each phase – such as attack, where the envelope generally rises from 0 volts to the highest voltage it can output – is a stage. You might also hear it used to describe the number of sample stages in a BBD (Bucket Brigade Delay), described elsewhere.
  • Stage Fright
    What a finicky modular synthesizer experiences when we try to perform live with them.
  • State Variable Filter
    A state variable filter (SVF) is a common design for synth filters. This design lends itself to allowing low pass, high pass, and bandpass all being available simultaneously. Another side effect is that they are not prone to oscillating at high feedback (resonance) settings, although some have certainly figured out how to make this happen. The Oberheim SEM (Synthesizer Expander Module) filter is perhaps the most famous state variable design. I have been told this design introduces a lot of phase shift on output, which can add coloration.
  • Step
    Step is often used interchangeably with stage (see above), especially when talking about sequencers.
  • Step Sequencer
    This usually refers to a type of sequencer where you step to and pause on a stage, enter the note (and possibly the duration) for that stage, move on to the next step, and so forth.
  • Strike
    This term appears on several Make Noise modules, although it has been creeping into the general lingo. Some filters, amplifiers, and low pass gates (LPGs) that use or simulate vactrols (a light sensitive resistor placed next to a light source such as an LED, allowing a voltage to be turned into a resistance to control a parameter) may have a strike input. When you flash an LED at a light sensitive resistor, it does not change the resistance instantaneously and stay there – instead, there is some delay as it glides to the desired resistance. When you turn the LED off, the resistance may not go instantaneously to full; instead it might take a brief moment to decay. These characteristics are useful for creating percussive sounds and attacks. The purpose of a strike input is either to pass just a short pulse, or to allow you to re-attack while the LED is otherwise still on.
  • Subharmonic
    A circuit that divides the fundamental harmonic of the incoming sound to produce lower frequencies, and therefore subharmonics. The most common is an octave divider or sub bass circuit that divides creates a subharmonic by dividing the fundamental by 2 (some can also create a subharmonic two octaves below the fundamental by dividing it by 4). Click through for more details, including examples of instruments based around subharmonic generators.
  • Suboctave
    A module that creates a new tone one or two octaves below the fundamental harmonic – the “pitch” – of the sound coming into it, to emphasize the bass. (Subharmonics are discussed in detail elsewhere in this glossary.) This tone is usually a square wave, although some clever modules may create something more sine-like, or that more closely resembles the original waveform.
  • Subtractive Synthesis
    The most common synthesis technique: You start with one or more oscillators outputting waveforms with a large number of harmonics, and then pass this mix through a filter that removes some of the harmonics to create the desired sound or timbre. This modified tone is then sent to an amplifier that adds articulation to the note by varying its loudness. Click for a link to a video I created on patching a typical subtractive synthesis voice.
  • Sum
    To sum is a fancy way of saying you added two (or more) things together; the sum is the result. It usually is used in the context of adding together control voltages, although it can also be used for audio or even mixes of harmonics. The opposite is difference, which subtracts one input from another.
  • Sustain
    This is a common stage of an envelope generator where a voltage – usually being sent to a filter’s cutoff frequency or an amplifier’s level – is being held a steady level while a note is still being held down. The knowledge that a note is being held is usually provided by a gate signal, that stays high as long as a note is held down, although some envelope generators may have a dedicated time control for how long the sustain stage should last. Envelopes that contain sustain stages include the ADSR (Attack/Decay/Sustain/Release) and AR (Attack/Release, which usually assumes a sustain stage); these are described in more detail elsewhere.
  • SVF
    A state variable filter (SVF) is a common design for synth filters. This design lends itself to allowing low pass, high pass, and bandpass all being available simultaneously. Another side effect is that they are not prone to oscillating at high feedback (resonance) settings, although some have certainly figured out how to make this happen. The Oberheim SEM (Synthesizer Expander Module) filter is perhaps the most famous state variable design. I have been told this design introduces a lot of phase shift on output, which can add coloration.
  • Switch Trigger
    Some systems – such as the original Moog modular – use an s-trigger (switch or shorting trigger) instead of a normal gate, which was a wire that was shorted to 0 volts ground, like the closing of a switch wired to ground. You cannot interconnect these two systems without some form of conversion between the two, which can be as simple as a special cable.
  • Switching Power Supply
    A switching power supply starts by directly converting the incoming high-voltage AC signal into a high-voltage DC signal. They then rapidly switch that output on and off to average a lower output voltage. This switched voltage is then smoothed out to create a constant DC supply at the desired voltage. Switching power supplies tend to be lighter, cooler, and less expensive, at the cost of often higher noise – both in the output voltage, and in radio frequencies (this is why they are often surrounded by a shielding cage). Many are moving to a hybrid power supply that combines a switcher with a small linear supply or regulator to get the best of both worlds.
  • Sync
    Sync can have two different meanings, depending on whether we're talking about oscillators or about clock signals. Some oscillators support a mode where they reset their waveshapes to the beginning when they receive a signal from another oscillator. If there is not a precise octave relationship between the two oscillators, the result is a modified waveform that has been reset prematurely, following the frequency of the second oscillator. You can create some very cool “ripping” sounds by modulating the frequency of the slave oscillator; a simple AD envelope works well. In the context of timing, when you are synchronizing sequencers or drum patterns, it is common to send a master timing or sync signal around the modular for all the relevant modules to follow. This is typically a gate or trigger signal. Click through for more details on both.
  • Sync24
    Sync24 is an alternate name used for the Roland-created standard DIN Sync, which sends a clock signal at the rate of 24 pulses per quarter note at the current tempo. Korg equipment used a variation of this running at 48 pulses per quarter note, also known as Sync48.
  • Synthesizer Expander Module
    The Oberheim SEM (Synthesizer Expander Module) was one of their earliest products. It was an entire synthesizer voice – two oscillators, two simple envelopes, VCA, and a very popular two-pole state variable filter design with a knob that crossfaded between low pass, notch, and high pass outputs plus a separate bandpass setting – in a cube-like case. Most often today, when a modular manufacturer uses the magic letters "SEM", they're referring to a filter meant to emulate that in the original Oberheim synth. Click through for a little more history, as well as a link to Tom Oberheim's current company which is still producing SEM-derived synths.
  • Threaded Inserts
    A common system for mounting modules into a case is called sliding rails or nuts. A number of nuts are inserted into these channels, which can then be slid to any position to accommodate the mounting whole spacing of your modules. Some don’t like this system, so they replace the nuts with strip of metal inserted into the channel that have been pre-drilled for the standard Eurorack mounting hole spacing. They may be drilled for 2.5 or 3 mm screws; pay attention when buying the rails or a case that has them pre-installed. Click for the pros and cons of this system.
  • Threshold
    A threshold is generally a voltage level a signal needs to cross before a module takes an action. For example, when the output of an envelope follower (a module that creates a voltage that corresponds to the current level of an audio signal) rises above a threshold level, then its gate signal will go high indicating a note has started. When the output of the envelope follower falls before a threshold (which may be the same or different than the note-on threshold), then the gate goes low, indicating the note should be finishing.
  • Through-Zero Frequency Modulation
    TZFM is the abbreviation for Through-Zero Frequency Modulation. Think of a patch where you feed the output of one oscillator (the modulator) into the frequency control voltage input of a second oscillator (the carrier). As the waveform output of the modulator rises above zero volts, it is added to the normal pitch control voltage for the carrier, and the pitch of the carrier goes up. As the waveform output of the modulator goes below zero, it is subtracted from the normal pitch control voltage, and the pitch goes down. But what happens if the result of subtracting the modulator from the pitch control goes below zero volts? In an oscillator that explicitly says it implements through-zero frequency modulation, the carrier will start playing backwards – in essence, a negative frequency. This generally produces a more pleasing result, and is a desirable characteristic for an oscillator. Click through for a few more details.
  • Timbre
    This word is often used to describe the unique tonal characteristic of a sound you are creating, separate from its pitch or loudness. Different sounds, by definition, have different timbres. When you change a parameter of a sound that changes its tonal characteristic – such as changing the filter cutoff, pulse width, amount of wavefolding, etc. – you are changing its timbre. The timbre often changes during life of a note. Click through for additional flowery language about this.
  • Tini-Jax
    This is a special design of jack made by Switchcraft that is used by Buchla (and many of their clones) to carry audio signals. They are 3.5mm in diameter, but differ slightly physically from a common 3.5 mm jack. 1/8” plugs would be loose in when plugged into a Tini-Jax jack; a Tini-Jax plug might not fit into or might even damage a 1/8” jack.
  • Tracking
    Tracking usually refers to how well an oscillator follows the pitch control voltage (CV) sent to it. As the voltage rises, the oscillator “tracks” it and produces a higher pitch. Most (but not all!) synths follow a 1 volt per octave system where a rise of 1.00 volts on the pitch input should produce exactly a doubling (one octave rise) in the oscillator’s pitch. If this is indeed what happens, the oscillator has good tracking. If the oscillator goes slightly out of tune, it is considered a tracking error, or to have poor tracking. Sometimes you will find voltage-controlled filters have a “tracking” switch for a CV input where the pitch of the filter’s corner frequency only rises at 1/3, 1/2, or 2/3 of the corresponding change of the pitch input. This can prevent high notes from sounding too bright without the bass notes sounding too dull. Sometimes you will find voltage-controlled filters have a “tracking” switch for a CV input where the pitch of the filter’s corner frequency only rises at 1/3, 1/2, or 2/3 of the corresponding change of the pitch input.
  • Transistor Ladder Filter
    This term is often used to describe the design of the much-loved Moog low-pass filter, which is still held up by many as being the gold standard in low pass filter sound. Moog actually received a patent for this design (it has since expired); many of their competitors either outright copied it or did their best to emulate it.
  • Transpose
    In the simplest terms, to transpose the pitch of a musical line is to shift it up or down by a fixed number of semitones or octaves. This is sometimes referred to as “chromatic” transposition. A more sophisticated variation is “scalar” transposition where each note is shifted by a set number of scale steps; this differs from chromatic transposition because some scales may have differing numbers of semitones between steps than other scales. Click through for details on matching the transposition range of different oscillators.
  • Tremolo
    This is the effect of varying the amplitude (loudness) of a note. A way to create this effect on a modular synth is to patch a low frequency oscillator (LFO) to one of the control voltage inputs on an amplifier. Tremolo is different than vibrato; the latter is a warbling in pitch rather than loudness.
  • Triangle
    The triangle is a common synthesizer waveform. When selected for the output of an oscillator, it was a more mellow sound than the standard square or sawtooth waves, with fewer and weaker higher harmonics. It is also a popular output for low frequency oscillators (LFOs), as it produces a relatively smooth up and down variation in whatever it controls, while being easier to create than the even smoother sine wave.
  • Trigger
    A trigger is a very short electrical pulse signal, rising from 0 volts to a standard level such as 5 or 10 volts for a few milliseconds before falling back to 0 volts. It is often used to start or “trigger” the playback of a percussion sound, including starting an envelope generator. They can also be used to pass clock signals around a synth so connected modules all know when a note (or finer subdivision of a note) starts. A trigger usually has a fixed duration, compared to a gate signal which also rises from 0 volts to a higher voltage and falls back to zero again, but which stays “high” a variable length of time depending on the length of a note.
  • Tune
    The act of adjusting the pitch of a synthesizer’s oscillator (the main pitch-generating element) to match another oscillator, instrument, or reference is known as tuning it.
  • TZFM
    TZFM is the abbreviation for Through-Zero Frequency Modulation. Think of a patch where you feed the output of one oscillator (the modulator) into the frequency control voltage input of a second oscillator (the carrier). As the waveform output of the modulator rises above zero volts, it is added to the normal pitch control voltage for the carrier, and the pitch of the carrier goes up. As the waveform output of the modulator goes below zero, it is subtracted from the normal pitch control voltage, and the pitch goes down. But what happens if the result of subtracting the modulator from the pitch control goes below zero volts? In an oscillator that explicitly says it implements through-zero frequency modulation, the carrier will start playing backwards – in essence, a negative frequency. This generally produces a more pleasing result, and is a desirable characteristic for an oscillator. Click through for a few more details.
  • U
    Rack-mounted equipment usually follows a standard set of dimensions, including 19” for width, and a “rack unit” (or U for short) for height equaling 1.75” per U. Many common modular synthesizer formats follow the rack unit system for standardizing module height – such as 3U (3 x 1.75 = 5.25”) for Eurorack, 4U for Buchla and Serge, and 5U for classic modular Moogs (sometimes referred to as MU for Moog Unit).
  • Unbalanced Audio
    Most audio signals are passed around on cables with two wires: one for the voltage that represents the audio vibrations, and one for ground. This arrangement is often referred to as unbalanced audio. Click through for details about its cousin, balanced audio.
  • Unipolar
    Many voltages in a modular synth – including the output of an audio oscillator, and most low frequency oscillators – fluctuates between positive and negative voltages. This is known as a bipolar voltage. Some voltages – such as the output of an envelope generator – only vary between 0 volts and some maximum positive voltage; this is referred to as unipolar. Click for more details.
  • Unity
    Also stated as "unity gain", this means a signal passing through will have the same level on output as it did on input. This is sometimes stated as a multiplication factor of 1.0 (as unity = 1).
  • V-trig
    There are two common ways to pass a “gate” signal around a modular synth: either a S-trig (Switch or Shorting Trigger) that simulates connecting a signal to ground, or a V-trig (Voltage Trigger) – also known as a trigger or gate – that sends a voltage to a higher level when a note is depressed or a drum is triggered, and which returns to zero volts when its done. V-trig is by far the most common format; S-trig was used on the original Moog modular systems but was not widely adopted going forward.
  • Vactrol
    A vactrol is a light depending resistor (LDR) placed next to a light source (previously an incandescent bulb; nowadays an LED). As the light gets brighter, the resistance goes lower. This is a great way to add voltage control to what would otherwise be a resister in a circuit. What makes people excited about vactrols is that the relationship between the light and resistance is nowhere near linear or instantaneous: It takes some time to slew up or down to the desired resistance. These ringing and settling characteristics are useful for creating percussive sounds and attacks. Click for more details.
  • VC
    One of the core concepts of a modular synthesizer is that one module can control another’s actions. Since a module can’t (yet) reach over and twist a knob on its neighbor, it does this through the idea of voltage control: a voltage level you send to a module adjusts one or more of its parameters. The clearest case of this is pitch: the voltage level you send to the to an oscillator determines what pitch it plays. The more voltage controllable parameters a module has, the more you can animate its sound by connecting it to controllers and other modules that output varying voltages. Click through for links to good introductory articles and videos on voltage control.
  • VCA
    A Voltage Controlled Amplifier (VCA) controls the amplitude of a signal passing through it by scaling or attenuating it in response to a separate control voltage input. It is most commonly used as the last stage in a patch, articulating when we can hear or not hear a sound the synthesizer is producing. Click through for more details and uses.
  • VCF
    A Voltage Controlled Filter (VCF) is the most common tone-altering module in a modular synth. It typically reduces the strength of select harmonics or overtones, changing the tonal balance of a sound. Click for more details.
  • VCO
    The Voltage Controlled Oscillator (VCO) is the main sound generation module. It produces a waveform (a pattern of vibrations in the air) that repeats – “oscillates” – at a certain frequency, which is the pitch of the note it is playing. A Voltage Controlled Oscillator allows you to set that pitch with an incoming voltage. The most common standard is for a change in 1.0 volts to result in a change of one octave in its tuning (Buchla modules use 1.2 volts per octave; with “linear” oscillators a change of 1 volt results in a change defined by a constant number of cycles per second, rather than a musical interval such as octaves). Tuning controls on the front of the module set the specific pitch you will hear for a specific voltage. Click for more details.
  • Vector Rails
    This is a common piece of hardware used in cases for Eurorack format modules. These horizontal rails that the modules mount to have a groove that runs along their length. You can insert square-shaped nuts that slide along these grooves, allowing you to move them to the required position to match up with the holes on the front of your modules. Or, you can insert “threaded strips” into these rails that have been pre-drilled and threaded. The hole pattern in these strips match the Doepfer standard that most modules adhere to (although their are some that don’t match up, such as Gotherman and Analogue Systems).
  • Vector Synthesis
    A synthesis technique where four user-selectable waveforms are mixed together using a quad panner before the result is sent on to a filter or other processing. This mix should be voltage control. Although there are a few quad oscillator modules, and several waveform modules that can crossfade between adjacent waves inside a table, I’m still waiting on a true vector synthesis oscillator to appear in a modular synth. In the meantime, click for a link to an article I wrote about the creation of the Prophet VS.
  • Velocity
    This parameter describes how fast you depress a key on a keyboard, or how hard you strike a drum trigger sensor. Some MIDI to CV (control voltage) converters will output a separate voltage for this parameter, allowing you to route it to filter cutoff, envelope length, etc. Some trigger interfaces will produce a separate voltage or gate output that can be used as an accent when triggering drum modules.
  • Vibrato
    A usually fast warble in the pitch of a note. This can be accomplished by patching the output of an LFO into one of the voltage controlled frequency inputs of an oscillator.
  • Vocoder
    Vocoders attempt to impress the harmonic structure of one sound onto another sound. The modulating sound is broken down into a series of frequency bands, and envelope followers measure how strong the content of each band is. A second carrier sound is then sent through a bank of bandpass filters usually tuned to the same as the frequency bands used for the modulator, with the output of their envelope followers controlling the strength of carrier signal allowed to pass through the bandpass filters. Click for more.
  • Voice
    This is one of those words that have been co-opted to have many meanings. It is often used to refer to a synth sound or patch. Indeed, early Oberheim instruments that could produce two or four sounds at once where called the Two Voice and Four Voice. Musicologists may be familiar with the term "voicing" as referring to the distribution of notes in a chord, or of notes and chords between different instruments in an ensemble; alternatively, sometimes you will hear the act of creating presets as “voicing” the instrument.
  • Voltage Control
    One of the core concepts of a modular synthesizer is that one module can control another’s actions. Since a module can’t (yet) reach over and twist a knob on its neighbor, it does this through the idea of voltage control: a voltage level you send to a module adjusts one or more of its parameters. The clearest case of this is pitch: the voltage level you send to the to an oscillator determines what pitch it plays. The more voltage controllable parameters a module has, the more you can animate its sound by connecting it to controllers and other modules that output varying voltages. Click through for links to good introductory articles and videos on voltage control.
  • Voltage Controlled Amplifier
    A Voltage Controlled Amplifier (VCA) controls the amplitude of a signal passing through it by scaling or attenuating it in response to a separate control voltage input. It is most commonly used as the last stage in a patch, articulating when we can hear or not hear a sound the synthesizer is producing. Click through for more details and uses.
  • Voltage Controlled Filter
    A Voltage Controlled Filter (VCF) is the most common tone-altering module in a modular synth. It typically reduces the strength of select harmonics or overtones, changing the tonal balance of a sound. Click for more details.
  • Voltage Controlled Oscillator
    The Voltage Controlled Oscillator (VCO) is the main sound generation module. It produces a waveform (a pattern of vibrations in the air) that repeats – “oscillates” – at a certain frequency, which is the pitch of the note it is playing. A Voltage Controlled Oscillator allows you to set that pitch with an incoming voltage. The most common standard is for a change in 1.0 volts to result in a change of one octave in its tuning (Buchla modules use 1.2 volts per octave; with “linear” oscillators a change of 1 volt results in a change defined by a constant number of cycles per second, rather than a musical interval such as octaves). Tuning controls on the front of the module set the specific pitch you will hear for a specific voltage. Click for more details.
  • Voltage Trigger
    There are two common ways to pass a “gate” signal around a modular synth: either a S-trig (Switch or Shorting Trigger) that simulates connecting a signal to ground, or a V-trig (Voltage Trigger) – also known as a trigger or gate – that sends a voltage to a higher level when a note is depressed or a drum is triggered, and which returns to zero volts when its done. V-trig is by far the most common format; S-trig was used on the original Moog modular systems but was not widely adopted going forward.
  • Wave
    This is the pattern of vibrations – up and down fluctuations in voltage – output by an oscillator. Different patterns generate different sounds.
  • Wavefolder
    A wavefolder is a very specific design of waveshaper that uses a comparator and some other circuitry. What they do is look to see if the wave goes above (or below) a specific threshold. When it does, instead of clipping off the top and bottom of the wave, they create a mirror image of it and reflect that portion of the wave back upon itself, creating more high harmonics and interesting spectra in the process. Click through for more details on how they work.
  • Waveform
    This is the pattern of vibrations – up and down fluctuations in voltage – output by an oscillator. Different patterns generate different sounds.
  • Waveshaper
    It would be a bit obvious to say “a circuit that changes the shape of the waveform going through it”, but that is the point. Waveshapers often have specific goals in mind, such as converting an incoming triangle wave into an outgoing sine wave, or to add tube-like soft clipping to the peaks and transients of waves. Many waveshapers are simply intended to mangle (er, add higher harmonics to) waveforms in interesting ways, creating noisier (er, more complex and bright) harmonic spectra to create new sounds.
  • Wavetable
    This term can have two related but slightly different meanings. A digital oscillator often produces sound by reading a table of numbers in order, jumping from the level described by one number to the next. This table of numbers describes one cycle of a wave, and therefore is often called a wavetable. Many digital oscillators have multiple wave tables lined up, and can move between these tables – either by jumping suddenly (which the original PPG Wave synths did), or by crossfading between them (what most digital wavetable oscillators today do). Some people refer to each table as a “wave” and a set of individual waves as a wavetable.
  • West Coast Synthesis
    The so-called "West Coast" approach to synthesis – traditionally associated with companies such as Buchla and Serge – is often based around adding harmonics to simple waveforms, rather than removing (filtering) them from complex waveforms. This is often accomplished by using a pair of oscillators (sometimes combined into what's called a "complex oscillator") where one modulates the frequency (FM) or amplitude (AM) of the other; another common West Coast module is a waveshaper or a wavefolder. You may also find two-stage envelope generators such as an AD or AR (often called slope generators) rather than four-stage ADSRs, as well as more of an emphasis on control voltage manipulation, A common feature is also voltage controlled amplifiers that have low-pass filters built into them, creating what's known as a Low Pass Gate (LPG). The West Coast approach also embraces non-traditional controllers, such as touch plates and the such. Today it's common to mix both East Coast and West Coast approaches in the same system.
  • wet
    A sound with effects (such as reverb) mixed is referred to as "wet"; a sound with no effects is referred to as "dry." Effects units or mixers often have wet/dry mix amounts that set the ratio between the original, unprocessed sound and the fully-effected sound.
  • wet sound
    Sometimes people will say a filter has a “wet” sound. This usually refers to a fewer-than-4-pole filter sound – often low or bandpass – with resonance turned up a bit, but not to the point of self-oscillation. It’s a sound that is popular in acid house and other similar techno styles. I reminds one of a vowel-ish vocal sound with a lot of moisture and pronounced formants.
  • White Noise
    Noise is a random signal that does not have a distinct pitch, such as hissing, breath noise, or the sound of wind or the surf. Noise is often described by different “colors” such as white, pink, red, or blue which have different frequency distributions. White noise has equal power per unit of frequency (such as every 1000 hertz), resulting in a brighter, hissier sound. Click for a Wikipedia link to graphs and audio examples.
  • 303
    The TB-303 Bass Line by Roland became a cult favorite in Acid House and other flavors of EDM (Electronic Dance Music) for its rubbery, slithery synth bass sound. Many attribute the sound of the 303 to its filter design; click for more details.
  • 808
    The TR-808 Rhythm Composer by Roland created all of its sounds using analog circuitry. When it first came out, it was not well loved, as the analog sounds weren’t realistic enough. But later, music styles such as House and Hip-Hop adopted its big, booming synthetic sounds. When a module says it recreates “808” drums, this is the instrument they are trying to emulate. Most copied is the 808 kick drum sound, which tends to be a low-pitched, long-decaying sine-like wave often with a snappy attack.
  • 909
    The TR-909 Rhythm Composer was the follow-up to Roland’s now-revered TR-808 (see above). It combined digital samples for the hi-hat and cymbal along with the 808’s analog sounds, and has also become popular. When a module says it produces 909-like sounds, this is the instrument it is referencing.

I don’t claim to know everything, but I do like to learn; please feel free to add to, correct, or request definitions in the Comments sections. I’m trying to focus on terminology that pops up while working with modular synthesizers, although there is inevitably some crossover with other parts of the synth world.

Feel free to link to this glossary if you think it would be useful to others. Please do not copy and paste it to your own site or documents; it literally took me months to create the first version, and I plan to update it regularly – so link to it instead to catch those updates.

15 Comments

  1. Jason Herring

    Love the new glossary here! Didn’t find an entry for multi-tap delay or multi-tapped delay. I’m still not sure what those are or how they differ from standard delays. I know there are some in the modular world. I know Sputnik makes one, Doepfer makes a multi-tapped BBD and Intellijel now has the Rainmaker. Perhaps consider adding it. Thanks.

    Reply
    • Chris Meyer

      Thanks for the kind words! And good suggestion for multi-tap delay – it’s now on the list to tackle soon.

      Reply
  2. Jason Herring

    Noticed a minor spelling error in the second sentence of AC Coupled definition. “(scuh as the output of an oscillator”. I’m assuming “scuh” is supposed to be “such”.

    Reply
    • Chris Meyer

      Good catch – thank you. I had already fixed it in the full definition, but had missed it in the short version.

      Reply
  3. Jason Herring

    Noticed two more copy errors on the “L” page.

    Under “Line Level”, “a typical oscillator signal in a modular synthesizer is +/5 to +/-8 volts.” I’m assuming you meant “+/-5 to +/-8 volts.”

    also

    Under “Logic Functions”, this sentence is repeated twice in the paragraph: “A common logic function is OR: If either signal A or signal B is high (on), then output a high gate signal (on); otherwise output a low gate (off). Another is AND: If and only if signal A and signal B are both, then output a high gate (on); otherwise, output a low gate (off).”

    Sorry to keep mentioning these little things, as I know this glossary was an exhaustive effort on your part, but I know you would probably want them to be correct.

    Feel free to delete these error correction comments if you don’t want them unnecessarily sticking around on your blog for years to come.

    Reply
  4. Chris Meyer

    Good eyes! I appreciate the corrections. Both are fixed now.

    Reply
  5. Reek Havok

    Thanks for sharing this Chris! This is really great and I’ll point lots of people in your direction!

    Reply
  6. Rob Kam

    When a filter or sound is described as wet?

    Reply
  7. Pablo Perez

    A nice one to add would be “Function Generator”. Thanks for the great glossary!

    Reply
  8. John Wise

    Thought you might add some details about a “Reset Gate” as the topic is not very well covered anywhere I can find.

    Reply

Submit a Comment

Your email address will not be published. Required fields are marked *