xoxos explains the model:
impulse is driven by ‘pitch’ which is a % for event per sample at oscillator pitch. tracking is implemented but architecture is geared towards percussion synthesis.
the event % is shaped with a ‘rise’ envelope that lowers the chance for events to immediately follow other events (ie. hysteresis, good for emulating ‘larger beans’). when rise is locked to pitch it can be shifted by +/- 2 octaves. ‘tail’ multiplies the % after the rise period to reduce longer gaps.
impulses are decay-stage enveloped and consist of either the envelope contour or enveloped noise, low pass filtered for dynamics performance, then routed to a bank for 5 bandpasses (# of bands can be reduced to save cpu).
Stoq is available as a freeware VST instrument for Windows PC. Download it here (1.35 MB).