Finally a working polyphonic MIDI to CV converter with auto tune.

video upload by Craig Barnes

"I've been working on this polyphonic MIDI to CV converter for about 2 years. I've built several other polyphonic MIDI to CV devices, but I needed an 8 note 16 bit device for accuracy. So previously signals like modulation, bend, interval, detune were all generated on separate CV lines. This converter combines all signals onto a single wire for each VCO and filter. So in total there are 24 CVs generated, 8 gates, 8 triggers, 8 velocity CV's, plus 8 spare CV lines if needed.

The Teensy has a feedback loop from each VCO via a 16 way mux chip and during auto tune each VCO in turn is fed into the Teensy and the frequency of 8 notes from each VCO is sampled and corrected against the correct frequency. The difference is then stored in a table and the remaining 120 corrections are extrapolated from the 8 samples. These are then stored into the SD card and reloaded at boot time.

It accepts 5 pin DIN MIDI and usb MIDI or it can act as a MIDI host to a usb keyboard. I hope to make it the basis of an 8 note analogue polysynth that actually stays in tune.

Functions are controllable over MIDI

https://github.com/craigyjp/16bit-8-n..."