The other way to make a voice. Where the source–filter model filters a buzz, FOF (Xavier Rodet's Fonction d'Onde Formantique, the engine inside CHANT) builds each formant out of grains: a tiny damped sinusoid at the formant frequency, fired once every vocal-fold period. The grain's decay sets the formant's width; its soft attack sets the skirt. Overlap the grains from successive periods and the formant appears — pitch-synchronous granular synthesis, and the classic way to synthesize a convincing sung voice. Related to VOSIM, which builds formants from pulse trains instead.
A shorter attack widens each formant's skirt (brighter, buzzier); a longer one narrows it (purer, more hollow).
sing a note (a s d f …) — each keypress is a stream of formant grains