hm, well of course b700 waveform data was digitally generated and stored, but i am really not sure which synthesis operations were/weren’t performed in digital domain. (the ‘4th computer’ mentioned in that description might have been some bespoke collection of ICs interfacing with PROM waveform data? i really don’t know.) one processor ran MIDAS, one executed a sort of MARF-like control generator section. in any case it was a truly hybrid system and could not be easily emulated, in its totality, by one program.
i did quite misremember how much of the source code was indeed written in C though. the guy i was thinking of was aaron lanterman and he posted the code here: http://users.ece.gatech.edu/~lanterma/buchla700/
… but IIRC it is mostly MIDAS code, BIOS for the editor, C libraries, &c. do let me know if you spot anything that looks like an FM calculation.
when i next get a chance i will have a look at the schematic as this thread has rewoken my curiosity about the instrument.