Polyphonic Pokey MIDI
One of the features of the MIDI Pokey synth is the ability to have one MIDI channel control all the Pokey voices polyphonically. That allows it to play chords directly from a standard MIDI keyboard without any fancy processing in between. The Pokey has four voices, so it can play four note chords. It can also do three note chords plus a melody line, and any other permutation of four. Making it work was just a matter of deciding how to route multiple notes to multiple channels.
Each new key pressed looks for an “off” voice in the set of four. If there is an open spot, the new note takes it. If all the spots are full, and there is no room at the inn, the oldest note gets kicked out by the newest.
Test Sequence
This is just a little test sequence to make sure the logic works correctly. If the voice stealing doesn’t work properly, then the first cascade of notes will not work. If the age-based note prejudice doesn’t work properly, the final cascade will not work. So far the output is passing.
To stop the channels from modulating each other, each has to have its volume cut down to a fourth. This makes the volume envelopes a lot coarser. I made a quick file of the smoothest possible volume fades that can happen at this level. Keep in mind that with only one voice playing at a time it can be four times this smooth.
March 17th, 2009 at 4:01 pm
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