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Analogue Systems RS300

CV-to-MIDI Converter
Published September 2004
By Paul Nagle

Analogue Systems RS300

No, we haven't got that the wrong way round... it really is a CV-to-MIDI converter. 'But why would you want such a thing?' you might ask. If so, read on and find out...

Hands up those of you who, on skimming the contents of this magazine, assumed this review involved a MIDI-to-CV converter. If so, take a closer look. Analogue Systems have produced something rather more unusual here; something that might require a little thought before its potential is appreciated. If you have pre-MIDI synth gear that works on Control Voltages (CVs), you may well find this latest addition to the RS Integrator modular synth interesting.

Description & Menus

The RS300 module is just under five inches wide, or 24 units of horizontal pitch, the measurement system used by various modular manufacturers including Doepfer and Analogue Systems (1HP equals a fifth of an inch). A MIDI Output socket and no less than 10 voltage inputs provide clues to its raison d'être. Of these, eight are CV inputs and the remaining two are trigger inputs. When in use, a small red data LED flashes to confirm that MIDI data is being generated.

The module is crowned by a 2x20 backlit screen which, in combination with the Edit knob and Cancel button, serves to access a series of menus. Rotating the Edit knob displays menu pages and to enter each page, you simply push the knob. On reaching a page in which values may be updated, turning the Edit knob performs this action. At all times, the Cancel key returns you back one level. Despite the interface's menu-driven nature, the navigation system remains quick and effective to use, and will be instantly familiar to anyone who has ever used a modern digital effects unit or synth; it's just that this style of user interface is much less commonly seen on Analogue Systems' gear. The final item on the panel is a Trigger Mode switch, which comes into play when MIDI notes are generated — more of this later.

The top-level menus are named as follows:

  • Input 1-8
  • Trigger/Switch
  • Memories
  • Special Options
  • Show Inputs

With only a couple of exceptions, each of the CV inputs behaves identically. Sub-menus are provided to specify the input voltage range and the type of MIDI message that should be generated. Each may be defined independently, with four possible voltage ranges to choose from: -10V to +10V, -5V to +5V, 0V to +10V, and 0V to +5V. From these voltages, a variety of seven-bit MIDI messages can be generated, such as pitch-bend wheel messages, aftertouch data, MIDI Continuous Controller (CC) messages from controller 0 to 127, MIDI note data (although from CV 1 only — see below), and velocity information for the aforementioned note data (again, see below). If you want an accurate translation of your input voltage to MIDI output, you should specify the range correctly. For example, if you are using the signal from an envelope whose level is between 0V and +5V, specifying a range of 0V to +10V will effectively compress the output into a range covering only half the possible values, because your envelope will never reach the peaks you have told the RS300 to expect.

The first two CV inputs have additional functionality not present in inputs three to eight. CV 1 offers the intriguing possibility of generating MIDI notes, whilst voltages received at CV 2 can be translated into velocities for those notes. If you do not use CV 2 in this fashion, all the output notes will have a fixed velocity specified within the menu. In order to gain the maximum useable range from your input, notes can be transposed by ±36 semitones.

The Trigger Mode switch (see inset picture, right) on the module's front panel governs how notes are triggered. Set this switch to Trigger and note length is determined by the duration of gate signals received at the Note Trigger input socket. Each gate signal creates a new MIDI note whose pitch is obtained from CV 1. In this way you can play MIDI synths via any synth that works on the octave-per-Volt CV system, provided that they are equipped with CV and Gate outputs. In practice, the RS300 did not respond well to fast trills from my Roland SH101 keyboard, but from an analogue CV sequencer such as my ARP 1621, triggering was precise and reliable.

Analogue Systems RS300

Creating MIDI notes in this way is straightforward enough, but wouldn't it be great if you could do so from a pure voltage source, one that lacks an associated trigger — like an LFO? With the RS300, you can. You simply flick the Trigger switch to its 'Free Run' setting and then navigate through the CV 1 Keyboard Settings menu until you arrive at the 'Note Sequencing' option. This sub-menu contains two settings for trigger generation. In the first instance, whenever a new note is detected, the previous note is turned off before the new one is played. In the second instance, the new note is turned on before the previous one is released. Thus, the second method generates legato or overlapping notes, which some synths can use to introduce portamento effects.

To set the length of these 'free-running' notes, a 'Free Run Note Hold' option is provided with values from 0.1 to 12.7 seconds, plus an 'infinite' setting — when this option is selected, the last note generated will receive no note-off event. One bonus of the note-hold parameter is that you can make a note that lasts a specific time, which is great when used with effect-type patches or with slow attack envelopes. I found that triggering was far more precise when the RS300 generated the note on/off events in this way, as opposed to receiving the gate information as described earlier. Those trills were faithfully rendered every time!

In cases where the module is having difficulty interpreting an unstable input voltage, the Note Delay parameter allows a period of between three and 50 milliseconds for it to stabilise before deciding which note to generate. In most cases, I found I was able to use the minimum setting.

Finally, there is a calibration routine for notes, based on a fixed range of three octaves (note that this is designed for octave-per-volt analogues). The module arrives ready-calibrated, so you may not need to do this. However, if you do, and have a three-octave C-C keyboard, simply select the 'Apply 0V To Input 1', press the Edit button and play the lowest note. Then select 'Apply 3V To Input 1' option, press Edit again, and play a note three octaves higher. My Roland SH101 has only 2.5 octaves, so I employed its transpose function to send the required range. You can't fool the calibration with voltages in a different range; I contemplated creating an inverted keyboard effect by sending a high voltage first and a low voltage second, but the module rumbled me and aborted the operation. The calibration is for generated notes only — CV 1's Input Voltage range selection is ignored when notes are being produced. Finally, a 'Show Keyboard Input' sub-menu displays the note detected.

The Trigger/Switch input (shown in the inset pic above) is the final one to require explanation. It is activated by a voltage blip such as a pulse wave or short envelope, and is capable of generating MIDI program changes, various MIDI on/off pedal controllers (sustain, portamento, soft pedal, and so on), a percussion note, or MIDI clock.

If you choose to generate a program change, you can specify one program to be sent when the voltage is high and another when it is low. Of perhaps more value, you could generate a specific MIDI note complete with velocity and MIDI channel (this option defaults to MIDI channel 10; the designers clearly had percussion triggering in mind).

For me, the most useful option in the Trigger/Switch menu is the ability to generate MIDI Clock. This covers an impressive range of tempos from 0 to 900bpm and has a variable 'Clocks Per Beat' parameter to set the number of incoming pulses per output MIDI beat. I used it to synchronise MIDI drum machines to my vintage sequencers and use all the tricks analogue offers in terms of tempo modulation.

Memories, Special Options & Show Inputs

There are 40 user memories in which to store your configurations. As the function of specific MIDI CC numbers varies from synth to synth, you will probably allocate one or more of these memories for each synth you plan to control with the RS300. As the RS300 has no MIDI In socket, the only way to select programs is via the menu system. I did wish for some means to do this remotely, but at least the menu is uncomplicated, with Read, Write, Edit Name and 'Erase All' options, as you'd expect.

The Special Options menu allows you to set the MIDI channel of the module, which is a global setting and not stored within user memories. You must therefore change the channel manually when controlling different synths or, alternatively, use a rechannelise function on your sequencer if you have one. Also located here is the MIDI Data Rate parameter, with settings of low, medium or high. The RS300 produces controllers, notes and aftertouch as accurately as MIDI allows. But since MIDI is a serial protocol, your synth might struggle under the onslaught of eight streams of dense information. If your source voltages are derived from riotous LFOs, wild Sample & Hold outputs or quickly sweeping envelopes, and then you further add to this load by banging in some notes on the keyboard, timing may suffer. In such cases, experimenting with lower data rates can be a lifesaver.

This menu also allows you to call up the current version of the operating system (version 1.1, dated 07/07/04, in the case of the review model) or reset the unit to its factory defaults.

The Show Inputs menu option, as the name suggests, brings up all eight CV inputs on a single screen. If the RS300 is being used to produce MIDI notes, the note value is shown. An asterisk appears in the top left-hand corner of the display whenever a gate is received at the Note Trigger input. Similarly, a small 'T' appears in the bottom right-hand corner when a voltage is detected at the Trigger/Switch input — a valuable visual reference. In all other cases, the numeric value of the event being transmitted is shown.


Now we're familiar with the inputs and menu system, let's take a look at some of the things you might do with the RS300. I've always shied away from the phrase 'limited only by your imagination', but the possibilities offered by this module are truly far-reaching. A few examples might make the value of this module clearer...

The review unit was supplied in one of Analogue Systems' stand-alone wooden cases, with its own power socket. Of course, if you're wiring the module into an existing modular system, a version without the case and power supply is also available.The review unit was supplied in one of Analogue Systems' stand-alone wooden cases, with its own power socket. Of course, if you're wiring the module into an existing modular system, a version without the case and power supply is also available.I've always felt that analogue sequencers had many advantages over (the majority of) their digital counterparts, so the opportunity to generate notes on my modern gear from my venerable ARP 1621 was one not to be missed. The ARP is a 16-step sequencer that can be divided into two rows of eight steps, which I did here. I connected the first row into the CV 1 input and connected the ARP's Gate output to the Note Trigger jack. Finally, I connected the second sequencer row to the CV 2 input of the module, specifying velocity as its output. Hitting Run on the sequencer produced a stream of MIDI notes and gave me full hands-on control of the note values and velocities via the ARP's sliders. When I drafted in a second sequencer generating MIDI controllers via the other CV inputs, all the marvels of analogue sequencing were at my fingertips — but they were now recordable into Cubase for further tweaking and arranging.

I then moved on from notes to controller generation. The possibilities offered by having up to eight analogue modulation sources generating MIDI controller curves are fascinating. I dug out the manuals for various synths in the studio — including my Access Virus, Korg Prophecy and Novation K-Station and Supernova II. Having decided on the parameters to control, I connected a series of outputs from my Digisound analogue modular synth. I then sat back agape at the most unusual and complex sounds I had ever heard emerging from my virtual-analogue synths. For example, directly modulating eight of the Virus' filter parameters using a series of LFOs resulted in a swirling pad to die for — the Virus is great, but doesn't have eight LFOs of its own! In some cases, I had to reduce the RS300's MIDI Data Rate before my synths drowned under the amount of data my analogue modular was sending them. Some of the most outlandish and experimental sounds were achieved by selecting controller numbers at random, connecting my voltage sources, then tweaking liberally. Forbidden Planet, here we come!

Lastly, I tried running some of my MIDI gear on Clock information generated in the analogue domain. I love my collection of Korg Electribes, but often wish they had a clock output with which to synchronise my older gear — such as the sequencer in my faithful Roland SH101. As the SH101 transmits gate information when its sequencer is running, I connected this output to the Trigger/Switch input. I was then able to generate MIDI Clock and run my drum machines at the LFO rate of this simple monosynth, although I had to manually hit Run on the drum machine, since the RS300 does not provide a MIDI start command.


Analogue Systems have produced a module that I always hoped would exist one day. True, Doepfer's A192 also converts voltages to MIDI controllers — but to my knowledge, the RS300 is the first to generate MIDI notes in this way as well. Producing streams of notes from analogue origins opens up a whole world of extravagant sweeps and warbles which can make you look again at even the blandest and most forgotten-about MIDI gear in your studio. Similarly, the ability to generate a clock signal, then slave MIDI drum machines and sequencers to it has advantages that modular freaks will already be well aware of.

Best of all, from my perspective, is the RS300's ability to generate MIDI controllers. By directly controlling synth parameters, you can create mutant sounds and modulations that are unachievable with the synth alone. If you want an LFO to sweep the filter overdrive of a Supernova, you now have a means to do it. And there are many more similar examples, depending on the gear you have.

You can probably tell that I'm impressed, and I won't deny it — but to make the RS300 even better, I'd have gone the whole hog and included a MIDI input capable of merging incoming data with that generated by the CV sources. You could then have used MIDI program changes to select user memories. Of course, this would have driven up the cost of a module that is already far from 'bargain basement', so Analogue Systems leave you free to add your own merge if you deem it necessary.

I'll end by saying the RS300 is a module whose value will be best appreciated by those of you with a diverse selection of voltage sources on tap. Combine it with a modular synth or analogue sequencer and you can expect hours of happy experimentation with your MIDI gear. If my examples have inspired you to think of better ones, then you are probably just the sort of person Analogue Systems had in mind when they brought this module into the world. You might discover a whole new perspective on driving synths (or software synths) from your analogue gear, which can't be a bad thing.

Published September 2004