Keypad poly 4 continues my tradition of wringing polyphony out of (ostensibly) monophonic keyboard modules (https://patchstorage.com/keypad-poly-3-keypad-polyest-polyphonic-synths-using-one-keyboard-module/). Keypad poly 4 is a five voice synth. The synth is a very simple triangle wave, with a variable duty cycle; I wanted a fancy reverb (hall reverb), but you could do a more elaborate synth with fewer voices or less fancy effects. I like the sound; it has a sort of orchestral quality to it (which is why I wanted the hall reverb).
Kepad poly 3 used triggered envelopes; you could play multiple notes at once, but each note lasted the same length. No more, kind of, with keypad poly 4: now gates matter.
Really, the gate is paraphonic, but the envelopes are not. It’s a weird hybrid. So, let’s say you play three notes, A, B, C, in that order. Even if you lift your hand from A and B, they will continue to sound until C is released. If, while still holding C, you play D, it will have an attack and decay stage to its envelope, then continue to share the sustain stage with C (and A and B). In practice, you might not notice it, but that’s how it works!
But one thing you might want to do with that arrangement is play a melody over a sustained chord(s), and you can’t, so: looper! I added a looper, because it was fun.
The way the looper works is a little weird, too, I guess: pressing the left stompswitch will arm it, but it will only begin recording when you play a note.
It has overdubbing, too, but it goes record > playback > overdub, so you need to press the left stompswitch again to begin overdubbing.
The middle stompswitch will cause the loop to play in reverse; holding down the middle stompswitch for 2 seconds will clear the loop. (I was originally going to use the third stompswitch for something else, but then I didn’t, and I’d already gotten used to this arrangement, so yeah, it would be easy to change the patch so each stompswitch had a dedicated function.)
(I also labeled the page with the looper, if you want an easy import page for a looper that goes into playback instead of overdub; to use it without all the weird arming stuff, just connect the flip flop directly below the looper to the looper record button.)
Left, latching –> loop record, overdub
Middle, momentary –> reverse
Middle, held for two seconds –> clear loop (the loop will begin to play in reverse, but that will be reset when the loop is reset)
Big ol’ keypad, tuned to D minor across five octaves.
ADSR controls for the envelopes.
Waveshape controls the duty cycle of the triangle wave. At the extremes, there are more harmonics added (it becomes almost sawtoothish); at the very extremes, it becomes a bit thin and reedy.
Tranpose allows you to transpose the keypad.
There’s a global LPF filter; you can change its frequency here (it’s a tone control, and it uses a multi-filter, so expect clicky as you adjust).
There are also decay and mix controls for the reverb, and a level control for the looper.