Here’s a demonstration of the finished mini-synth in action ... array (there’s more than enough CPU performance for greater polyphony, but it’s mostly just a matter that the input pads ...
[mitxela]’s polyphonic synth for the ATtiny 2313 does just that, using only two kilobytes of Flash and fitting inside a MIDI jack. Putting a MIDI synth into a MIDI plug is something we’ve seen ...