Topic: Adding vocal track
maybe you are aware of this, but to sum it up - it should be extremely straightforward to add vocal abilities to any 1-bit engine, as it seems, by the means of either microsamples (probably even 16-bit "bitmask" quantity in a register, and doing ADD HL, HL, is enough to express basic in-tune harmonics between distinct vowels) or to use, otherwise unused AY channels to sum it up additively.
Agemixer's Freestyler od SID MOS6581
Famous speech in U96 songs was actually STSPEECH.TOS utility on Atari ST, utilising AY-3-891x
Kecal, the routine from unknown author (it's NOT Oldsoft - Zdeněk Starý), was pioneering microsamples
https://worldofspectrum.org/archive/sof … -2-oldsoft
And recetly, I have found this, looks like it uses sequence of 32 Gameboy's 4-bit samples:
https://gbdev.gg8.se/wiki/articles/Game … d_hardware
Are You aware of any other routine of this kind? I think this is very unexplored area...
P.S.: UTZ, great posts about engine techniques and computer music history! I'm a biiig fan of what you are doing.