Augmented Poly-Paraphony: DSI Pro-2 paired with 4 analog Eurorack VCOs in paraphonic mode

video upload by thesrabbit

"The Pro-2 has been around a long time. I recently re-acquired one locally from a friend at a great price. The first time I had it I don't think I ever tried anything like this, but it makes total sense so it was time to give it a shot.

Simply put, I wanted to beef up the Pro 2's sound by supplementing its 4 digital oscillators with 4 meaty analog Eurorack VCOs. There are videos out there of this sort of thing, but only in monophonic mode, which is simple and straightforward to achieve. I wanted to give the Pro-2 two oscillators per note in paraphonic mode, for analog polysynth-esque chords.

The key to doing this is to recreate the Pro-2's per note articulation that it emulates by internally controlling the level of each oscillator's output at the DSP level, with a digital envelope per note that is the same shape as the one used for the actual VCA. The Pro-2 sort of behaves as if it has 4 VCAs, one for each note.

The best way to emulate that in Eurorack is to simply use real VCAs and envelopes for each note. So start with one VCO, run it into a VCA, and then control that VCA with an envelope, making sure that envelope's shape resembles the shape of the amp envelope on the Pro-2. Repeat the process 4 times, one for each VCO that will be paired with a Pro-2 oscillator. I used all analog modules for this. Roland System-500 oscillators, VCAs, and envelopes, Wavefonix CEM 3340 VCOs, Arcus Audio Dual VCAs, and a Doepfer dual envelope module. The output of each VCA is then mixed in a 4-to-1 mixer module, paying special attention to the levels of each oscillator, and then fed into a final VCA used specifically to attenuate the signal before passing it off to the external audio input of the Pro-2. It's of course difficult to match the shape of all 4 envelopes exactly, but there's no need to be too precise. I suppose I could have made things a little easier by using the Disting Ex's quad envelope. Then I could have dialed them all in exactly the same. All good though.

The NiftyKeyz is a paraphonic/polyphonic ready eurorack case/keyboard that has 4 CV/Gate outputs. Each subsequent key held down simply goes out the next CV/Gate output in sequence. So you can play for note chords, provided you have all the modules to do that. It also has MIDI I/O, so here the Pro-2 is being controlled via MIDI, despite it being the "main synth", whereas the Eurorack modules are supplementary. I would have preferred using the Pro-2's keyboard for this, but the NiftyKeyz has a puzzling limitation in the MIDI department. Essentially you cannot play it polyphonically from another keyboard without doing some sort of crazy MIDI channel mapping in between. I get why they do the 1 note per channel thing and it's indeed useful at times, but give us the option to use just one channel and behave as if we were simply playing its own keys. End side rant.

Waveshape is sawtooth for all oscillators. There's a little additional modulation going both to and from the Pro-2 and the rack with delayed LFOs, along with small amounts of "slop", so the digital oscillators aren't completely stiff.

Anyway, there it is, 2 oscillator per voice I mean note poly-paraphony on the Pro-2.

Oh, forgot to mention the Pro-2's headphone output is running into the Happy Nerding FX Aid Pro for that amazing lush reverb that's blended in. Other than that there's no other effects or processing."