Polyphonic Eurorack: First Try and Walkthrough

video by thesrabbit

"Here's my first attempt at polyphony within a modular system. I've got 4 distinct voices, each with its own oscillator, filter, amp, and envelope. To make things more interesting, I added a sort of sub-oscillator to the first voice, though it can sound quite dissonant depending upon when that voice is triggered.

There is a very detailed rundown after the demo "performance", but to summarize:
Each voice is a single sawtooth wave, with the addition of a square wave sub-oscillator on voice 1. All 4 oscillators run through their own low pass filter. The first 2 run through filters 1 and 2 on the System-500 521 dual VCF module. The 3rd oscillator runs through the LPF on the System-500 505 module. The 4th oscillator runs through the LPF on the MS-20 Mini. From there, each voice has its own VCA, and then the output of those VCAs are routed to the System-500 530 module, which acts as a stereo mixer. Voices 1 and 3 are panned to the left, 2 and 4 are panned to the right. This produces an effect similar to auto-panning. All four voices run through a BBD and spring reverb tank, which adds a ton of extra grit. Each voice has its own dedicated envelope generator. The first 2 have the System-500 540's envelopes. The 3rd voice uses a single ADSR from the Dreadbox Ataxia. The 4th voice simply uses EG2 on the MS-20 Mini.

I did my best to get a similar sound out of each voice, though it's far from perfect. However, that's really the whole point of this experiment: to do something that no standard polysynth can do.

In the demo, I've got aux sends setup in Logic to the Audiothingies Dr. A for delay, and for reverb I've got my favorite Alesis MIDIVerb II and Quadraverb combo. These effects run in parallel and were recorded in real time along with the dry output of my mixer. I tried to mix in the effects so that they're about 55/45 dry/wet.

Modules used:
Roland System-500: 512, 521, 505, 530, 540
2HP VCO (x2)
Polyend Poly 2
Arcus Audio buffered mult
Pittsburgh Modular Giraffe (x2)
Blue Lantern Subharmonics
Manhattan Analog DTM
Doepfer Dual VCA (x2)
Dreadbox Ataxia
Erica Synths PICO BBD
G-Storm Electro Spring Reverb Tank Driver
Korg MS-20 Mini"