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Doepfer MCV24

Multi-channel MIDI-to-CV Converter By Paul Nagle
Published March 2000

Doepfer MCV24

Even the most die‑hard analogue synth enthusiast must recognise the advantages to be gained by integrating their voltage‑controlled gear into a MIDI environment.

Despite the growing army of 'virtual' analogue synthesizers, large numbers of classic analogue synths are still used on a daily basis and remain highly sought‑after. This, coupled with a thriving new generation of analogue modulars, means that the demand for a 'one‑box' solution to integrate them all into a MIDI environment has never been stronger. Doepfer's MCV24 is a well‑specified MIDI‑to‑CV converter with 24 programmable outputs, clock and DIN Sync functions, and an extensive modulation matrix, along with built‑in low frequency oscillators and envelopes. Before you start wondering just who needs to control 24 analogue synths, however, note that only four of the MCV24's outputs produce 'high‑quality' control voltages for controlling note pitch; the rest are intended to carry trigger signals, modulation and envelope contours, or voltages derived from incoming MIDI controllers.


The Doepfer MCV24 is just a single rack space high and 3.5 inches deep. Its silver finish and mini‑jack (3.5mm) sockets suggest that it is designed to work in partnership with the company's own analogue modular systems. This is especially evident in the positioning of the 24 voltage outputs and two additional clock sockets, which are all packed onto the front panel. The rear panel is spartan in comparison, having just MIDI In and Out (no Thru), a programmable Sync output (for some older drum machines and Roland's TB303), the internal power supply socket (and switch) and a tiny adjustment screw for the display contrast. Once the MIDI leads are connected, you could plumb it into a rack and never need to grope around the back at all.

Doepfer have opted for software‑only configuration, freeing the user from having to poke about with a miniature screwdriver: all parameter changes are made with three continuous knobs and a 2 x 16‑character backlit display. From left to right, the knobs control Output selection, Menu navigation and Value editing. They are light, slightly notched and pleasant to use.

On The Menu

All operations are programmed via seven pages of menus, labelled A‑G, each with a different function. Each menu is accessed by turning the middle knob: (A) is Version Information, (B) CV Parameters, (C) LFO and ADSR Parameters, (D) Modulation Matrix, (E) System Parameters, (F) Global Sync Parameters and (G) Presets & Utilities. Wherever you are in the menu system, pushing down on the middle knob will take you back to the top level; pushing it again will return you to your current position. You select which of the 24 outputs to edit using the left‑most knob then alter values with the right knob, confirming them by a push — a neat system when you get used to it.

As it's hard to predict which synths the owners of such a device will be using it to control, very little is pre‑programmed at the factory. Therefore, the first step will be to customise it for the tasks it will perform in your studio.

Let's get the ball rolling by configuring the CV Parameters. The first thing to notice is that when any of the 24 programmable outputs is used to output a Control Voltage, this is actually derived from two Control Voltages, CV1 and CV2, which are merged internally to produce the final signal. These can be set up to respond to the various kinds of MIDI event you might send (notes, controllers, aftertouch, and so on) on any MIDI channel you specify. It's probably a good idea to keep these two CVs on the same channel or things can become very confusing.

In a typical example, we could set CV1 to carry notes and CV2 pitch‑bend information. Both CVs have their own slew generator (see the 'How Do They Do That?' box for more information) with an on/off status and a slew amount. Obtaining the classic portamento effect is a simple matter of adding slew to CV1.

In order to play the synth in the desired pitch range for your controlling keyboard, a 'base' note must be specified. Here, incidentally, Doepfer have deviated from common practice — you'd usually expect a clockwise turn of the value knob to increase a given value, but in this case a clockwise turn lowers the value. Having done this, the next step is to set up a keyboard zone, represented by a 'from note' and 'to note' range. Though you can play the synth over whatever range you want, if you are controlling multiple analogues from the MCV24, different zone ranges on the same MIDI channel can create a handy split keyboard effect. Your left hand could then play SH101 bass while your right performs a Minimoog solo (if you are lucky enough to possess these synths and the necessary dexterity). The velocity of incoming notes can be translated into a voltage appearing at (up to) four outputs of your choice, or it can directly modify elements of the built‑in ADSR envelopes, LFO modulation depth or slew rate.

By now we've defined the note CV and some associated velocity or controller mapping: next, the trigger mode should be set. Helpfully, the trigger output port is picked when defining the port for the note CV and if you forget which one you chose (which its quite possible, believe me), scrolling through the outputs using the leftmost knob will display a message to remind you. Up to four trigger outputs are available simultaneously; alternatively, if you prefer, an internal software envelope can be initiated instead. Various key‑priority options enable all the classic low‑note/high‑note and multi/single triggering of our favourite analogue synths to be achieved. To cap it all, there are two polyphonic modes which allow you to play chords using several analogue monosynths. Finally, a Retrigger Time value sets a delay between pressing a note and the trigger output being generated.

All this setting up is a lot to tackle and, thankfully, the initial bootup configuration is factory‑programmed so that MIDI notes received on channel 1 will send CV to the MCV24's Output 1 and a corresponding trigger to Output 13 (so at least you can get something happening right away). These two sockets are grouped together vertically, which I found a sensible convention for my own organisation of notes and triggers.

Doepfer MCV24 rear panel.Doepfer MCV24 rear panel.


Many MIDI‑to‑CV converters include software‑generated modulation sources — low‑frequency oscillators — and these are often simple affairs intended to add vibrato to the note voltage. The MCV24 goes way beyond this: its LFO and ADSR menu offers both an LFO and ADSR for every one of the 24 outputs. The LFO waveforms on offer are Pulse, Sine, variable Triangle/Sawtooth and two flavours of Random. Each LFO's frequency may be set at an internal rate or to divisions of MIDI clock, with a range going from semiquavers up to 15 bars! There's powerful rhythmic potential to exploit here using several MIDI‑sync'ed LFOs to control different synth parameters, and I'm sure you can think of some fun examples without my help.

An LFO parameter, 'Ratio', alters the shape of the basic waveform. Thus, if Triangle/Sawtooth is selected, a downward sawtooth can be morphed through triangle and then on to upward sawtooth with a turn of the value knob (a similar method is used in the Korg MS20's modulation generator). A further parameter, 'Offset Value', offsets the modulation polarity so that its centre point is either above or below zero. A practical use of this might be to simulate the way a guitarist adds vibrato, a positive offset being used to prevent the modulation going below the pitch of the root note.

LFO Depth may be varied dynamically via a MIDI controller (as set in the Modulation Matrix menu) or by velocity (in the CV Parameter menu). The only downer (and a surprising omission) is that there is no means of controlling LFO Speed in a similar way. Having lots of LFO shapes and the ability to bend their waveforms is very useful, but if you've chosen to work with analogue synths, having to plough through a menu system merely to alter modulation rate goes against the grain. As a workaround, with so many LFOs on tap, I reserved half a dozen of them, with differing speeds and waveforms, and simply chose the one that was closest to my needs at any time.

The built‑in envelopes are of the traditional ADSR variety. They aren't quite a replacement for dedicated hardware contour generators since they lack a really speedy response but, even so, there are useful jobs they could do in any analogue modular system. Setting each stage on the MCV24 itself was a little laborious because the value knob didn't seem to be able to cope with fast updates. I'm used to spinning a knob quickly to reach the upper or lower values, but here you need to be a little more patient. Envelope amount may be set directly or controlled via velocity or via a MIDI controller, using the modulation matrix.

Modulation Matrix

The Modulation Matrix Menu is a versatile means of routing MIDI events to voltage destinations. The MCV24 boasts six of these routings for each of its outputs, the sources being taken from aftertouch, pitch bend, and the standard list of MIDI controllers (mod wheel, data entry, sustain on/off, and so on). Setting up each routing is a matter of selecting the incoming MIDI channel, the event type (and controller number, if relevant) and the destination. Available destinations are the internal envelope's Attack Time, Decay Time, Sustain Level and Release Time, ADSR Depth, LFO Depth, Slew Rate and one called 'reserved for future expansion' (my fingers are crossed in the hope that this will be LFO Speed). As you can see, you could use separate MIDI controllers to set each envelope stage, which could provide a partial solution to the slow response of the value knob.

None of my grumbles would stop me from picking the MCV24 as the most flexible MIDI‑to‑CV converter around.

Dessert Menu

The final three menus are concerned with tasks you probably won't perform so often. In the System Parameter menu, you can assign a meaningful name to each of the outputs (you can still view the original output number by pushing the 'output' knob). Tuning mode is set here too, again for each output, whether it be Volt/Octave or Volt/Hz. This menu is also where calibration of the internal voltages CV1 and CV2 is performed. The options are quite comprehensive, and default to those more appropriate for Volt/Octave synths.

Gate on and off levels are set here, expressed as a percentage of the maximum voltage output. Most of the MCV24's terminology refers to note 'triggers' rather than gates and I've (mostly) stuck to this convention during the course of this review — see Part 7 of Gordon Reid's Synth Secrets series in SOS November 1999 for a fuller explanation of triggers and gates. The manual explains how to configure outputs for positive gates and for the negative 'S‑Trig' system favoured by Moog and Korg. With a maximum level of 10.6V on tap, it should be possible to create a trigger output to suit any application.

Incidentally, there are a few proprietary interfaces that the MCV24 won't talk to — Roland's DCB and the interface in EDP's Wasp come to mind — but other than these, it's adaptable enough to talk to most synths that are designed for external control. Remember the Sync connection at the rear? Well, the Global Sync menu is used to set divisions of an incoming MIDI clock so that old but popular drum machines by Roland (which used 'Sync24'), Korg (whose instruments used sync at 48 PPQ) or more obscure devices can all be clocked from this output. I didn't have any of these to try, but I was able to use the clock output and start/stop pulses (available from the front‑panel sockets) to sync an old Roland CR78 drum machine.

The Preset and Utilities menu offers, as you'd expect, a means of naming and storing your configurations for all outputs, in up to 16 memory slots. Presets may also be transmitted as System Exclusive data for storage into a librarian or sequencer program. Each Output's settings can be copied or exchanged with another and an initialise option, defaulting to Volt/Octave settings, completes this menu's functions and our tour around the bowels of the MCV24.


The MCV24 is Doepfer's contender for the title of Most Highly Specified MIDI‑to‑CV Converter On The Planet, offering a wealth of possibilities and few shortcomings. The four 'high‑quality' outputs (which convert MIDI data to CVs at 12‑bit resolution) gave stable tuning across a wide octave range whilst the remaining (8‑bit) outputs performed the task of carrying trigger or control signals well enough. Throwing in 24 software LFOs and envelopes is also generous, though I was frustrated that LFO speed could not be adjusted directly via MIDI. Another (minor) annoyance is the speed at which some of the values update as you turn the data knob. When tweaking the onboard envelopes or some of the other parameters, large increments which should be accomplished by a simple spin of the dial had to be done very slowly and deliberately otherwise no value change happened at all. I also suffered a couple of operational 'weirdies' — for example, a couple of times, for no reason I could discover, the trigger options seemed to be temporarily lost, and on several occasions the software envelopes stopped working. All was restored by pushing the value knob, at which point the MCV24 displayed 'recalculating data' and recovered itself.

None of my grumbles, however, would stop me from picking the MCV24 as the most flexible MIDI‑to‑CV converter around. For many people, its specification will evoke cries of 'overkill!' and certainly, for those who have only a couple of simple monosynths, this is the equivalent of cracking a nut with a steamroller. If, on the other hand, you have one or more of Korg's MS‑series synths, or just about anything modular, then all those voltage sources start to look very tempting. I did most of the review tests using my reliable old Digisound modular and a Korg MS20.

At time of writing, the full manual has yet to be translated from the German, though a useful introductory English manual is available. I needed to refer to the German version of the manual once (to find the correct settings to drive the MS20) and if it boiled down to a choice between having the MCV24 available now or waiting until the full English manual appeared, I'd pick the former option. It seems that Doepfer's mission these days is to pack in as many features as possible, yet keep the price affordable. Apart from the few software rough edges I've mentioned, it really does give unparalleled connectivity between MIDI and CV with no obvious corner‑cutting. Perhaps it lacks the reassuring 'quality' aura of Kenton's Pro 4 but, at almost £200 less, I can live with that. At some point in the future I will get round to merging my analogue modulars with my MIDI system. When I do, I can't currently think of any MIDI‑to‑CV converter I'd choose over the MCV24.

MIDI‑to‑CV Conversion — How Do They Do That?

Let's take a moment to consider the issues surrounding MIDI‑to‑voltage conversion — this might help explain some of the ideas that went into the MCV24's design.

MIDI is all about absolutes: every Note On is formed of numbers representing pitch and velocity. In a voltage‑based synthesizer, a note is formed from a 'control' voltage (CV) and a 'gate' or 'trigger' voltage. The former is continously variable, and sets the pitch, while the latter, which simply switches between an 'on' and an 'off' level, tells the synth when a note starts and stops so that envelopes can be triggered and the signal can pass through. It's pretty obvious that the accuracy of the pitch CV is the most important, since the output pitch is directly related to the control voltage. As long as the gate level is sufficient to trigger the envelope, a little variation won't hurt, but if the voltage controlling the pitch isn't spot on, the tuning is unstable. Any MIDI‑to‑CV converter, therefore, must be capable of precise voltage output.

MIDI data, though, is comprised of far more than just note information: controller, aftertouch and pitch‑bend data can all be put to good use if translated into analogue voltages. Though most of these are more sophisticated than simple on/off messages, they aren't as sensitive as pitch information. In the case of the modulation wheel, for example, MIDI convention has allocated this popular means of expression just 128 possible values, and if we translate these directly into voltages they become, well, steppy. The answer isn't merely to bump up the power of the MIDI‑to‑CV conversion process because the low resolution is at the MIDI end.

Doepfer's solution in the MCV24 is to include 'slew' generators at various points in the conversion process. Owners of modular synthesizers will be familiar with the concept of slew already, since slew generators are used to blur the divisions between notes to form portamento, for example. By using the same principle, the MCV24 is able to even out the harsh transitions inherent in low‑resolution MIDI controllers, so they sound almost as good as the smooth voltage changes produced by an analogue synth. Isn't progress a wonderful thing?

The MCV24 is equipped with four 12‑bit Digital‑to‑Analogue Converters (DACS), with the remaining 20 being just 8‑bit resolution. Some other MIDI‑to‑CV units offer higher resolution 16‑bit DACs, but I detected no tuning imperfections with the MCV24 when rendering MIDI notes to voltages, either at the more common Volt/Octave standard or the Volt/Hz settings used by some monosynths. The four 12‑bit outputs are intended for note operations, so you can play on up to four synthesizers independently. The 8‑bit outputs can perform a variety of other tasks and, if their internal 'slew' function is turned on, can conceal their lower‑resolution nature remarkably well.


  • 24 software‑configurable outputs plus Clock and Sync outputs.
  • Rackmountable with connections at front, so ideal for use with modulars.
  • 24 software LFOs and 24 software envelopes.
  • Six‑way modulation matrix for each output.


  • LFO speed not controllable via MIDI.
  • Knob response feels sluggish when performing large‑scale value updates.
  • Full manual not yet translated to English.


It's hard to seriously fault the MCV24, especially at the price. If you have an analogue modular or several other synths which would benefit from multiple voltage sources, this is a great way to plumb them into your MIDI studio.


£325 including VAT.