Interesting timing. Over on the Dark Side I'm designing an entirely digital music synthesiser - I always wanted a synth but VCO's and VCA's are so complex for us
digital types ! That handles six oscillators, eight ADSR's and mixing. Various waveform tables, ring modulation, frequency and amplitude modulation all done in around 44uS so far ( at 20 MIPS ), max freq 7812Hz at 64uS tick. Analogue output is by PWM and a simple RC network.
Memory usage isn't so bad, 256 byte sine table, ramp and square all derived from the phase accumulator. Code is around 1KB. Sampled / non-sine wave tables are what takes up the space.
A similar device, but not open source, is Savage Inovation's Soundgin(TM) which is the inspiration for what I'm doing ...
www.soundgin.com
That's based on a PICmicro 18F1320 running ( probably ) at 10 MIPS. The user manual there is a very good read for anyone interested in music generation. Very nice graphical control software available, and it's serially controllable. And it does speech !
Speed is the real key to good sound. Even the humble SOUND command does well at 4MHz but to get sine wave outputs there's a lot more to be done and multiplying to do amplitude modulation is quite time consuming.