MATRIXSYNTH: Polynorth - a hybrid analog/digital polyphonic synthesizer

Wednesday, July 31, 2019

Polynorth - a hybrid analog/digital polyphonic synthesizer

Published on Jul 31, 2019 Jon Petter Skagmo


"The Polynorth is my first attempt at designing a polyphonic synthesizer. It's got a completely analog filter section, combined with a powerful 200 MHz 32-bit microcontroller.

I've always wanted to build an analog polyphonic synthesizer, but they often end up being very large and complex because the size of the electronics pretty much scales linearly with the number of voices.

In many ways I think the filters are the hardest part of a digital synthesizer to get to "sound analog", so I figured out a good compromise would be to keep the filters analog and do all the rest with a microcontroller. The mostly digital architecture also has some important benefits:

- Flexible internal signal routing like a modular synth, but without a ton of patch leads
- More advanced modulation options (FM)
- Patch store/recall (including the routing)
- Much smaller size

I stumbled upon the SSI2144 filter, which is a modern remake of the classic SSM2044. It's very similar in many ways, but in a much more compact package and with better dynamic range, so a 6 voice synth could be made pretty compact. This is what kicked off the project.

The system architecture is explained in this block schematic."

See for additional details.

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