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.
- A-440This is the frequency in hertz (cycles per second) of the A above Middle C. It is often used as a tuning reference.
- ACIn modular terms, AC refers to a voltage that alternates between positive and negative values – such as the output of an oscillator.
- Alternating CurrentIn modular terms, AC refers to a voltage that alternates between positive and negative values – such as the output of an oscillator.
- AC CoupledAn 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.
- Buffered MultipleQuite 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.
- Active MultipleQuite 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.
- ADShorthand 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/DecayShorthand 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 SynthesisOne 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.
- ADSRAn 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/Decay/Sustain/ReleaseAn 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.
- AFGThe 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.
- Audio Frequency GeneratorThe 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.
- AftertouchSome 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.
- PressureSome 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.
- AHDSRThis 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/Hold/Decay/Sustain/ReleaseThis 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.
- AlgorithmThe different synthesis techniques that may be coded inside a software-based module is often referred to as the module's algorithms. Click through for a few examples.
- AliasingIf 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.
- AMAmplitude 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 ModulationAmplitude 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.
- AnalogThe 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 ORAn “analog OR” or “maximum” circuit looks at one or more incoming control voltages, and outputs just the highest value. The output of an analog OR can never be higher than the highest of value of any incoming voltage. This is a particularly good way to combine two envelopes, such as one with a fast attack and decay, and one with a slow attack.
- AND functionOne 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.
- ARThe 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.)
- Attack/ReleaseThe 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.)
- ArpeggiatorPutting 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.
- ArticulateThe details of playing a note – how forcefully you play it, as well as any inflections you may insert while playing that note – is known as how you "articulate" a note.
- Analog Shift RegisterAn 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.
- ASRAn 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.
- AttackThis 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.
- AttenuatorA control that can reduce the strength of a signal or voltage going through it.
- FaderA control that can reduce the strength of a signal or voltage going through it.
- Attenuator
- AttenuverterA 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.
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.
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.
Thanks for the kind words! And good suggestion for multi-tap delay – it’s now on the list to tackle soon.
I would personally love to see a video / using a multi-tap delay.
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”.
Good catch – thank you. I had already fixed it in the full definition, but had missed it in the short version.
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.
Good eyes! I appreciate the corrections. Both are fixed now.
Thanks for sharing this Chris! This is really great and I’ll point lots of people in your direction!
When a filter or sound is described as wet?
Good one. I’ll work on that.
Here’s an attempt: https://learningmodular.com/glossary/wet-sound/
A nice one to add would be “Function Generator”. Thanks for the great glossary!
Good idea, especially as there can be more than one definition. I’ll get to work on that.
Sorry it took me so long to do this: https://learningmodular.com/glossary/function-generator/
Thought you might add some details about a “Reset Gate” as the topic is not very well covered anywhere I can find.
Good suggestion!
https://learningmodular.com/glossary/reset/
A thing I don’t see mentioned is
Insufficient funds
Usually a result of gas
Hah! So true…
Amazing rescource, thanks very much for your work. Great for people (like me) just getting into modular and finding your way.
One suggestion was for ‘Polarizer’, unless it was listed under something else.
Good one! I’ll add that to the list – I cover the idea in other places, but don’t have an entry for this word.
Quite often, when manufacturers say they have a “polarizing” mixer etc., they mean inverting – so I created an entry for Polarizer and currently have it re-directing to Inverter: https://learningmodular.com/glossary/inverter/
If you find a case where a polarizer means a different thing than inverter, let me know and I’ll create separate entries for them. Thanks!
Excellent’ my suggestion would be to add Karplus–Strong string synthesis.
Thanks!
https://en.wikipedia.org/wiki/Karplus%E2%80%93Strong_string_synthesis?wprov=sfti1
Thanks for the suggestion! I’m finishing up a set of videos on the Rossum Morpheus filter this week, but when those are done, I’ll update the Glossary with your suggestion (and Tim’s, and whatever other ones come in this week).
Hi Chris,
Thanks for all of your amazing work. Your videos, articles and glossary have been extremely helpful and informative. I was looking for a definition for four quadrant multiplier in your glossary and didn’t see one. Maybe I missed it. If not, maybe it’s something worth conisdering.
Thanks again,
Alec
Thanks! I have glossary items for ring modulation and amplitude modulation; I’ll add cross-references so they appear for four and two quadrant multipliers respectively.
Four-quadrant modulation is another way of saying “ring” modulation. I added a separate entry for it to help separate it from the two-quadrant case of most amplitude modulation: https://learningmodular.com/glossary/four-quadrant-multiplier/
Thank you! What a great way to fill in the gaps.
This is great! Not only do you have a glossary, but I can learn by reading comments. Like a kid in a candy store!
I came in to find a definition of oscillator ‘spread’, which is not listed – yet…
Thanks.
Good one! I’m at Moogfest right now, but I’ll try to add that in the next few days. Thanks!
I’m surprised there’s no entry for ‘wave rectifier’.
Thanks for your work.
Good suggestion – I will create new entries for half and full wave rectifiers this weekend. Thanks!
Hey there,
Looking for a good description for “Just Intonation” if you have time to create one. Thanks!
Good one! I’ve put it on the short list to write.
Hi there Chris, i’ll throw a suggestion for “Burst Generator” into the pile. Thanks
Great suggestion! I’ve jotted it down and will add it this month.
A definition for “Compound Module” would be great !
I apologize that it took me so long to see your comment! I’ve added Compound Module to the glossary now. Thank you!
I came here to look up QUO which I think is a Quadrature Oscillator was just not sure if the U in the middle meant something on its on
QUO is just the way Serge abbreviates Quadrature Oscillator abbreviated that way. You will also see that abbreviation appear in the module name ChaQuO, which is Chaos Quadrature Oscillator. Based on your comment, I added that abbreviation to the definition.
I have two suggestions for the glossary:
Subharmonics
Transients
I suspect that subharmonics are any/all harmonics coming after the first harmonic?
Every time I think I understand what is meant by the word “transient” I come across it being used in a way that confuses me.
Thank you, Chris, for the time and effort you’ve put into this glossary. It’s been incredibly useful!
Hi, Bradley; thanks for the kind words. And thank you for the suggestions – I will them this week. But to quickly answer your question about subharmonics, they are harmonics below the fundamental, as opposed to above. We normally talk about harmonics existing at frequencies that are integer multiples of the fundamental note’s frequency; subharmonics are at integer divisions, such as 1/2, 1/3, etc. of the frequency.
This movie will help demonstrate subharmonics: https://youtu.be/NW1va8r8x2o
Thank you, Chris!
a BIG Texas sized thank you! I have to admit, even tho I’ve been an audio production hobbyist, eurorack is a completely different game altogether. I’ve struggled now for over 3 months(in my spare time). Do you have any recommended literature or videos for entry level noobs like me? Thank you again!
Thank you for the kind words!
I created my original Learning Modular Synthesis course exactly for people like you: https://learningmodular.com/register/learning-modular-synthesis-the-comprehensive-starter-course/
If you’re more comfortable reading, Kim Bjørn and I wrote Patch & Tweak, which includes begin-from-zero introductory material (as well as intermediate and advanced information): https://learningmodular.com/patch-tweak/
I just purchased Patch & Tweak from PerfectCircuit.com
I will read this a few times before beginning video course. Thank you!
Thank you for your support! I hope you enjoy the course. Let me know if you have any questions.
Bias. That word seems to have a number of possible uses. For example, Bias is the Gain knob on some VCAs only it’s not called Bias. It’s called Gain. To a newbie like me, this is very confusing and mildly frustrating. Could you possibly add Bias to the glossary and sort out the different usages/meanings?
Thanks.
Great suggestion. I’ll try to get to that in the next few days.
Thanks!!
The entry for Phasing mentions Terry Riley where I would have expected Steve Reich to appear, so I looked it up on wikipedia.
In 1965, influenced by Terry Riley’s use of tape looping and delay, the American composer Steve Reich started experimenting with looping techniques and accidentally discovered the potential of gradual phase shifting as a compositional resource.
I think Steve Reich deserves to be mentioned here 😉
You are correct! I will fix that. Good catch!
Wondering if “shift register” might be a good entry to add to the glossary.
Good suggestion! I have long had an entry for Analog Shift Register, and I thought I had it automatically copied over to just Shift Register, but I was wrong. So I craeted a new entry today. Thanks for the nudge!
maybe a voice for “retrigger” ?
i know it’s obvious but sometimes dumb people (——>me) approach this stuff..
thanks for your work
Good one – I’ll try to get to that soon. I have also been working separately on a “beginner” post on my Patreon channel about the differences between “envelope” and “function” generators, which is related.
And don’t worry about asking “obvious” questions – this stuff is NOT intuitive, and none of us were born knowing it – we ALL had to learn somehow, somewhere…
scale isnt in the glossary
The last W entry , did you mean …The word , rather than The wiard
I meant Wiard – a small modular manufacturer that created the original Woggle Bug (or Wogglebug, if you like): http://wiard.com/modular/300series/wogglebug/