One of the most attractive features of modular synthesizers is the wide variety of modules and functions available – especially in the Eurorack format. However, along with that variety has come freedom for manufacturers to choose how their modules operate…which can occasionally cause issues for users combining modules from different manufacturers. One of those potential variations is how they respond to control voltages for pitch. Virtually everyone agrees that a change in 1.00 volts equates to change of one octave (halving or doubling in pitch) for an oscillator – but how many volts does a module require to produce a particular pitch?
If there’s a difference between the modules you own, in most cases it can be dialed out with a module’s own pitch knob, or perhaps a transpose function in your MIDI to CV (Control Voltage) interface. However, there are occasions when you need the assistance of an additional module – often referred to as a precision adder or octave switcher – to settle disagreements.
I’ve been reading manuals, talking to a number of manufacturers, and measuring my own modules, and have built a couple of tables for your reference: one for the default settings of MIDI to CV converters, and another for how specific oscillators respond to voltage. As I learn more, I’ll keep amending this list. The goal is to give you a head start in understanding how modules you own or are considering buying might play together, and to prepare you to compensate for some of the differences you many encounter.
Middle C, Where Art Thou?
I know there’s a bit of ongoing debate about the subject of “Middle C”: Is it MIDI note 48 or 60? Do we call it C3 or C4? 8′ or 16′? Is its pitch 130.8, 261.6, or 523.25 Hz (cycles per second), or some other number?
Without trying to settle any of those arguments, for the sake of this post I’m going to use MIDI note 60 (3C hex), C4, and 261.6 Hz for Middle C, which will be our reference throughout the rest of this post. For oscillators that have their octave switch marked in terms of feet, I’m going to use 8′ as the reference, as it is used for when concert A (440Hz) is above Middle C (261.6 Hz). If you or your modules prefer a different reference or labeling system, please offset the numbers below accordingly.
MIDI to CV Converters
I included in this category modules and standalone boxes that convert MIDI to control voltages, controller keyboards that output both MIDI and CV, and semi-modular synths that have their own MIDI input as well as a CV output.
All of the numbers below are based on the default settings at power up, as from the factory. Most of these devices have a way to set octave or finer transpositions between MIDI and CV using their front panel, through jumpers on the circuit board (Expert Sleepers FH-1), by using a web application (Intellijel µMIDI), etc.
For MIDI note 60, the resulting output voltage for the following devices is:
| MIDI/CV Converter, Controller, or semi-modular synth | Voltage for MIDI Note 60 at default settings |
|---|---|
| Moog Mother-32 | 0.0 v |
| Expert Sleepers FH-1 | 0.0 v |
| Kenton Pro 2 (older model) | 1.0 v |
| Kenton MIDI to CV converters (current) | 2.0v |
| Mutable Instruments Yarns | 2.0 v |
| MST MIDI to CV Converter | 2.0v |
| Doepfer A-190-1, A-190-2, & MCV4 | 2.0 v |
| Doepfer A-190-4 | 3.0 v |
| Akai MAX25 | 3.0 v |
| Pittsburgh MIDI 3 | 3.0 v |
| Roland SBX-1 | 3.0 v |
| Intellijel µMIDI | 3.0 v (was 5v in older versions of the firmware) |
| Arturia MiniBrute, MicroBrute, BeatStep, and KeyStep | 4.0 v |
As you can see from the above, there can be up to five volts (which means five octaves) difference depending on which device you use to convert MIDI or a local keyboard to control voltages! If nothing else, I hope this gives you incentive to spend some quality time with your converter’s manual so you know how to change its response to better line up with your chosen oscillator(s).
Eurorack VCOs
Transposing your keyboard or MIDI signal is one solution, but what if you are driving two different VCOs that have two different voltage requirements to play the same note?
I’ve listed below a cross-section of VCOs, as well as a few semi-modulars than include external CV input for their own oscillators. I’ve assumed that any pitch controls are set to their initial or center position (usually 12:00), with no external modulation. Most VCOs will – with some slight tweaking – play a C with these settings when fed an integer number of volts (i.e. 1.00, 2.00, etc.), so I’ve noted the voltage they’d like to see to play the same note: C4 (261.6 Hz). If there is an octave switch, it’s set at either +0 octaves or 8’. When given a choice between High, Mid, or Lo ranges, I went with High, as the others are often LFO modes. I’ve also included a conservative summary of the front panel tuning ranges of each module, to give you an idea of you how much you can reliably twist a knob to dial in an interval from C or match one VCO up with another:
| VCO | Voltage for C4 | Coarse Tuning Range (octaves) | Fine Tuning Range (semitones) |
|---|---|---|---|
| Synthesis Technology E350 | 0.0 v | 07 (+4.5/-2.5 continuous) | 24 (+/-12) |
| Moog Mother-32 | 0.0 v | –– | 24 (+/-12) |
| Intellijel Dixie II+ | 0.0 v | 07 (+3/-4 in octave steps) | 12 (+/-6) |
| Intellijel Rubicon and Dixie II | 0.0 v | 11 (+/-5.5 continuous) | 12 (+/-6) |
| Verbos Harmonic Oscillator | 0.0 v | 12 (+/-6 continuous) | –– |
| Verbos Complex Oscillator (master; modulation requires 4.0v) | 0.0v | 12 (+/-6 continuous) | 10 (+/-5) |
| Expert Sleepers Disting mk2 modes 4-c and 4-d | 1.0 v | –– | 12 (+/-6) |
| AJH Minimod | 1.0 v | 04 (+/-2 in octave steps) | 16 (+/-8 or greater) |
| Roland 512 | 1.0 v | 04 (+/-2 continuous) | 12 (+/-6) |
| Make Noise DPO & STO | 1.0 v | 09 (+/-4.5 or more, continous) | 10 (+/-5) |
| Expert Sleepers Disting mk3 modes 4-c and 4-d | 1.0 v | 20 (+8/-12 in octave steps) | 12 (+/-6) |
| Doepfer A-110-2 | 2.0 v | 02 (+/1 in octave steps) | 12 (+/-6) |
| Doepfer A-110-1 | 2.0 v | 04 (+/-2 in octave steps) | 12 (+/-6) |
| Roland System-1m | 2.0 v | 05 (+2/-3 in octave steps) | 02 (+/-1) |
| Doepfer A-111 | 2.0 v | 07 (+4/-3 in octave steps) | 12 (+/-6) |
| Mutable Instruments Braids | 2.0 v | 08 (+/-4 continuous) | 02 (+/-1) |
| Waldorf nw1 | 2.4 v | 02 (+/-1 in octave steps) | 12 (+5/-7) |
| Pittsburgh Lifeforms SV-1 | 3.0 v | 17 (+/-8.5 continuous) | 16 (+/-8) |
| Arturia Minibrute & Microbrute | 4.0 v | –– | 04 (+/-2) |
| Erica Black Varishape VCO2 | 4.0 v | 10 (+/-3 in octave steps, plus +/-2 continuous) | 04 (+/-2 for VCO2; VCO1 does not have fine tune) |
At my arbitrarily-chosen default settings, when fed an integer number of volts the Synthesis Technology E350 plays roughly an E, while the Waldorf nw1 and the Make Noise DPO & STO play roughly a G. For the E350 and Make Noise VCOs which have a wide tuning range on their main pitch knob, I used the nearest C; the nw1 has a limited tuning range so I kept its in-between voltage.
As you can see above, the same voltage can result in an up to four octave difference in the resulting pitch. Most Eurorack oscillators have very wide front panel tuning ranges, and so you can merely dial out the difference, if there is any. But if you’re up against the limits of an oscillator’s tuning range just to get it in unison with another oscillator…and then you want to tune them to some other musical interval beyond that range…then you might have an issue. However, there is a solution.
The Takeaway: Consider a Precision Adder Module
Given the above, depending on your personal mix of gear, I think it would be wise for a modular synthesist to consider including a “precision adder” or other form of octave offset voltage processing module in their system. Split your pitch CV through a buffered mult, send one signal to one oscillator, and send a copy of this signal through your voltage processor to add or subtract the required number of volts before sending the signal on to your second oscillator. This is also a quick and easy way to add a precision octave switch to a module that otherwise just has a large continuous pitch dial (note: I’ve had oscillators that required retuning after changing their own octave switch)
Examples of octave offset voltage processors include the Doepfer A-185-2 Precision Adder, ALM/Busy Circuits ALM002 Beast’s Chalkboard, Frequency Central Trans Europa, algorithm 1-a (Precision Adder) in the Expert Sleepers Disting, or even the rare Analogue Systems RS-420. All are useful, and each has a different feature set that you have to personally weigh. The Disting is my current favorite as it has a very wide +/-9v (octave) range, and is cost-effective as the module can do other things when you don’t need an offset control. An interesting alternative is the Ladik Q-010 Easy Quantizer, as it includes octave and semitone offset controls as well as quantization feature.
Is the Sky Really Falling?
There’s a reasonable chance your given collection of modules already play together well, or can have their differences resolved with a twist of a knob. But maybe not.
In my case, I installed a bright shiny new Waldorf nw1 into my rack, connected the “KB” output from a Moog Mother-32 to its “CV” input, latched a low arpeggio on my controller keyboard…and was convinced either the Waldorf or my brain was defective, as I could barely get it to play anything other than its absolute lowest note. I almost pulled the Waldorf out of the rack and returned it.
As it turns out, the nw1 doesn’t respond to anything below 0v, while the Mother-32 thinks that’s Middle C. Even if I transposed the controller keyboard up, tuned the Mother’s VCO all the way down, and tuned the nw1 all the way up, I could barely get them in unison – and I wanted to nw1 to play a high sound over the Mother’s strong bass. Fortunately, once I figured out what was going on, I could patch around it and get back playing again. I’m just trying to share what I’ve learned with you so you can keep the flow going as well.
If you have details on any other modules I can add to this list, please pass it along – feel free to contact me publicly in the comments below, privately through the Contact form at the bottom of the About page on this site, or on the Learning Modular Facebook page.
An issue that’s perplexed even more users is matching up modulation voltage ranges between modules: 0-5v? 0-8v? 0-10v? +/-5v? +/-10v? This is a little more free-form since modulation can do so many different things, but in the future I plan to tackle at least how to patch around the differences.
The default for the µMIDI is now (as of firmware 1.14) 3V, but the tuning is adjustable using the online configuration utility.
Thank you – I’ll edit the article from the old default of 5v to your new default of 3v. The online utility is a very nice idea too, by the way.
Tried the Doepfer adder No luck .I dont think its possible >>>
I’m sorry to hear that. Could you elaborate what problem you’re experiencing? I’ve heard some say they’ve had power supply issues with the Doepfer.
yes the mother is odd,I got a erica synths picoM the converts the tracking voltage,but the Octave is still differant just gonna deal with it>> The crazy thing is I got the vermona qMI2 and when sending CV s to the Moog everything is perfect?? all the pitches are the same ?
Its just the sequencer that is weird …
Now I wanna run the Mother seq into the qMI2 to run what ever its sending out to, via CV to Midi>>>
I wanna talk to vermona about getting the CV into the QMI2 to play though it>> it has a Gate IN but Needs CV and a way to route it to the outputs, its a really solid interface>>
You mention the E350 but it’s not listed on your table. Anyway, good work, it gave me some ideas which will be utilized in further designs.
Good catch! It got bumped off the top of the table during an edit; it’s back again. Glad the article and tables overall were useful.
Just ran across this article thanks to a fellow Facebooker when I posted about this same problem earlier in regards to my Microbrute and eurorack stuff being way out of whack when using the Micro to control it.. My Doepfer A-110-1 at range 0 is in fact 2 octaves off just like your table says, and my EMW VCO 104 has to be dropped an octave to keep up with that.. If I did my math right I think that makes the EMW stuff 3v for middle C?
Just double-checking: The A-110-1 is playing two octaves higher than you expect, and then the EMW 104 is one octave below the A-110-1? (I don’t have access to an EMW VCO…) If so, then you’re correct, the EMW 104 seems to want 3.0v for middle C.
Now Im questioning my math haha. If I unplug the Microbrutes CV and set the Doepfer’s range to 0, and just let the two VCO’s drone, yeah I have to tune the EMW down an octave and it matches the Doepfer.. However when I plug back in the Micro’s CV input, and drop the Doepfer to -2 to match the Microbrute, the EMW seems to be an octave higher than the Doepfer and Microbrute now? Maybe its expecting 1.0v for middle C?? This stuff was so much easier with MIDI haha.. But after 20 something years I finally started my first modular and its sooooo much more fun than all my old analogs and VAs Ive had over the years..
Oooh never mind that one, I think I get it now.. The EMW only has a coarse tune knob that goes from -12 to +12, where the Doepfer has the coarse tune as well as the octave range switch. I should’ve just bought another A-110 like I wanted, but the EMW was about $50 cheaper and the feature set is almost exactly what the A-110 is minus the Range switch. Live and learn I guess! Ill have to look into the Doepfer Adder module now I suppose.
I’m having this problem too, most notably when I’m trying to take the CV out from Yarns and plugging it into the 1v/oct in on my m32. So, the precision adder is good for making the audio drop to the right octave once it’s processed by the osc; how about using a dc offset to adjust the voltage before it goes into the oscillator? Would that work too? I’ve resorted to just connecting my m32 to Yarns via the midi thru but that seems like cheating… Thanks for this article!!
You would need a precision adder to accurately add the voltage offset to the output of your Yarns – if you just use a CV mixer, there’s a chance that it’s full signal/not attenuated mode may not be precisely x 1.000, introducing its own tuning issues.
There’s more buffered multiples appearing that also this addition; the 333 from Frap Tools as well as the middle section of a Xaoc Devices Warna II are good examples. Then you could plug a CV source into one input and your Yarns into the other.
Awesome – thanks so much! So the signal flow is: Yarns -> precision adder -> m32’s vco 1v/oct, right? This article will be regarded by future scientists much like how we revere the Rosetta Stone today!
You’ve got it.
If you’re curious, when I want to drive one VCO (like the Mother’s), I often use mode 1A in a Disting; when I want to drive multiple VCOs, I’ve been using an Analogue Systems RS420, as it has multiple outputs with separate output switches.
But there are plenty of other solutions from Doepfer, Ladik, soon Industrial Music Electronics, and more.
Thanks for those recommendations! I’m kinda in love with the Beast’s Chalkboard! Seems like everyone else is too since I can’t find it anywhere! But then again, maybe this is a good excuse to finally get a disting…
Oh, yeah – Beast’s Chalkboard is very good too. They are hard to find. I tried to buy one used, but it literally fell out of the box while being shipped to me; I got an empty tube.
Hah! The curse of the Beast! I found one on Detroit Modular just now. Score! Thanks again, This problem has seriously been vexing me for a while…
Hi! I really want to truthfully understand this 1V/Oct thing right. These tables are confusing me a little. So I have to ask, for example, if I have Erica Synths Black Wavetable VCO then by giving 4V signal to its 1V/Oct input I will get this C4 (261 Hz, MIDI note 60) on it’s output, right (0V – C0, 1V – C1, 2V – C2 etc.)? And with Moog Mother if I give into its 1V/Oct input the same 4V signal I get what? On the tables there is written that for C4 I have to give 0V. But doesn’t Moog Mother work like this: with -5V I get C0, -4V – C1, -3V – C2, -2V – C3, -1V – C4, 0V – C5, 1V – C6 etc.? So for C4 I need to give -1V? Thank you!
You’re correct on the Erica Black VCO.
The Mother-32, in contrast to the Erica, wants 0v (not 4V) to play Middle C. If you send 4v to the Mother, it will play a note 4 octaves higher (1v/octave), so C8.
If you are patching an external pitch CV into the the Mother, you can use the front panel keyboard and octave transposition buttons to offset it down a few octaves to help bring it in tune with the Erica. But not all semi-modular synths or VCOs have easy octave transpose buttons like that, unfortunately; that’s why I like to have precision adder modules that have easy octave offsets (like mode 1A on a Disting).
Thank you for your fast replay! I want to understand this Moog Mother 1V/Oct situation. As I understand it takes -5V to +5V signal into its 1V/Oct input? Am I wrong counting octaves and voltages like this: with -5V I get C0, -4V – C1, -3V – C2, -2V – C3, -1V – C4, 0V – C5, 1V – C6, 2V – C7, 3V – C8, 4V – C9, 5V – C10? Why The Mother-32 wants 0v (not -1V) to play Middle C?
Don’t assume the bottom of the range (-5v) automatically means C0. The real cornerstone is 0v = middle C; work up and down from there.
The Mother can offset from here. The 0v=middle C rule works when the Octave LED is at 4 (the default at power-up) and when you press the top C on its front panel keyboard. If you press the low C instead, it will be offset down 1 octave. And the octave transposition works as well.
I see. Thank you very much for this clarification!
Is the SSF GND CTRL considered a precision adder? If so, would this be a good alternative to these other modules?
Thanks, I’m a big fan!
To work as a precision adder for pitch control, a utility module such as this one has to precisely pass through the input at a ratio of 1.0000 – any deviation will not work. This requires a lot of trimming and calibration at the factory to pull off, so if a module can do it, it will usually not be shy about saying so. I just read through the manual for the Ground Control and it does not make any mention of using it as a precision adder, so I’m not going to make the assumption that it will. (If nothing else, the bias voltage control does not have exact 1.0000 v increments to act as octave offsets, which would be another shortcoming for this application.) But I’ll ask them to be sure.
Thanks a lot for the reply and answer. I guess I didn’t grasp the concept on the first read.lol I forgot it would need to be in exactly 1.0V steps.
Got an answer back from SSF: “GND CTRL is not accurate enough by my standards as a precision adder. The main function of the module is for scaling and level feedback.”
On my Braids I could only “roughly” identify 7 octaves (using Mordax Data) and even then my C7 only flashed in occasionally and the C8 was never seen as the note octaves danced around. So I’m wondering if this might be calibration, though it was recently calibrated with a tight 1V and 3V signal and/or the power subsystem of my rack (which I have about 20% headroom).
I find that the Koma Elektronik Attenuator Cables work great for dialing down a voltage a very accurate 2V.
While I don’t have the reading for coarse octaves yet I can tell you that the following oscillators see a C4 note at these values:
WMD Spectrum = 1V / Telharmonic = 1V / Mangrove = -1V / Kotelnikov = 2V / Orgone Accumulator = 4V / 4Vox = -1V / Loquelic Iteritas = 1V / E950 = 0V
I’m glad to hear the Koma attenuator cables are that easy to use – I was afraid such as short slider would be overly fiddly to use!
And thanks for the numbers on your other oscillators – I’ve been wanting to fill out the tables more. What octave setting did you use on the Spectrum for your measurements? (Or for any of the others that had octave switches?)
A note about the Mordax Data and my problem reading higher notes, the manual of the Data states that its range is 27.50 Hz – 2,960 Hz (spans notes A0 to ~F#7) – problem solved on that side by reading the old manual.
A lot of tuners bug out with too high or low of a pitch. I’ll use DATA to confirm Middle C, but then count the octaves by ear as I go above or below.
More Oscillator info:
Spectrum = 1V. Octave was set at the #0 position (all lights off). There are 7 octaves under course and roughly 3 semitones for fine.
Telharmonic = 1V. Flux CW, Centroid CCW, Tonic/Interval/Degree set at 12:00. You can get close to 4 shaky/wobbly octaves. Not meant to be fine tuned 🙂
Kotelnikov = 2V. Octave switch in top #2 position. The pitch knob offers adjustments for 11 semitones.
Mangrove = -1V. Barrel/Air/Formant at 12:00. Formant out. 8 octaves for course knob and 12 semitones for fine.
Orgone Accumulator = 4V. Course set at 11:00 for C4. 4 octaves for course knob and 5 semitones for fine.
4Vox = 0V. Please disregard previous voltage report. Octave set to +0/+0. Classic Waves/1 voice. 8 octaves with course and 2 semitones with fine.
Loquelic Iteritis = 1V. Switch set to VO. Must set to 2V for SS/PM oscillator modes. 7 octaves with course and 12 semitones with fine.
E950 = 0V. Bank A Wave 0:1. 5 octaves with course and 4 semitones with fine.
Thanks for the additional details. I like to center the octave switching and coarse tuning so users know they have equal range above and below that reference to bring one VCO in line with another.
That’s where I set mine, although with the Orgone Accumulator that wasn’t possible.
I am currently designing my own MIDI to CV module and I am quite distressed by the lack of standards. What should I equate my C4 to?
Hi, i have a mother 32 and a erica synths wavetable vco and i am having this problem so i bought a erica pico mscale. Now when i plug mother kb out into 1v/oct wavetable vco it does the complete opposite than before. I could get 1-4 octave on mother keyboard now I get octave 5-8. I am only learning but i just feel like i am getting no where. My mother plays a low bass and my wavetable vco is playing higher notes
I don’t have an MScale, but it sounds like you might have the sections backwards? One adds 5 volts; the other subtracts 5 volts.
I’m connecting my modular to Ableton Live via 2HP MIDI — specifically to Plaits. The note I play in Ableton are not correct through the modular. The farther I get from C, the worse it gets. Any idea what I’m missing?
Either 2hp MIDI is not outputting the correct voltage for the note you’re requesting, or Plaits’ tracking is out and needs to be re-calibrated.
A cool thing about the MIDI Toolkit for Live 10 is that it includes (I believe) tracking correction, where it can compensate for this error.
Really useful article!
I was trying to decide on the default C4 voltage output of the analog variant my new product, the SynthiMuse :
http://www.synthimuse.com
and your info nailed it for me.
Many thanks
Gerry
A very nice and useful article indeed. I’ve been using the Doepfer Precision Adder for some time now, but its workings still puzzle me from time to time. I’ve found that the voltages at the input are all summed including their octave switches. I tried to momentary transpose a melody line (at about a fifth up) and found it hard to work properly. When engaging the attenuater it is very easy to bumb or nudge into the knob thus wrecking up the carefully dialed-in pitch. I really have to be careful not to get into these not so happy accidents. I want to apply this in a live situation but I’m a bit unsure about this. Could you recommend other utility modules that do the same job (momentary transposition of thirds, fourths and fifths) but with less danger of accidentally detuning?
There’s a few modules that come to mind. I use a Klavis CalTrans in my live case for quick semitone and octave transpositions. A few other modules like the Frequency Central Trans-Europa and upcoming AJH Synth Mini Mod Precision Voltages also have semitone knobs.
An alternate approach is to pre-program a few voltage offsets you want on a device like the Make Noise Pressure Points or another touch controller or sequencer that lets you pull up a preset voltage, and sum that with your normal pitch CV using a precision adder. That way touching this separate device will bring up preset intervals.
First thank you so much for sharing all your modular knowledge !
I end up here because i’m facing something absurd : playing Moog Minitaur with Moog Mother 32 via CV doesn’t work great at all…
That’s amazing… since it’s the same brand.
I almost can’t hear anything coming out of the Minitaur until i reach the highest octave of the Mother 32. until this, it’s very very low…
So, following your advices, i think Disting mk4 is the solution, right ?
If you’ve ever heard of that problem, or have any other idea, i’ll be very happy to read it 🙂
Thanks again for your time and all the informations you share !
Yes – the Precision Adder algorithm in the Disting (even the mk1!) will allow you to do octave offsets, that will hopefully line them up.
NB the Arturia Keystep has a configuration option for which MIDI note equals 0V. HOWEVER, the hardware is unipolar and will only produce voltages from 0 to 10 volts. So if you set 0V to middle C, you can only play notes at or above middle C.
That’s a frustrating choice. I guess the hardware was already designed to be unipolar, and they added that offset in software thinking it would be better than nothing…