He started off making an AVR synthesized guitar, but [Erix] ended up with much more: a complete six-voice AVR wavetable synthesis song machine that’ll run on an ATMega328 — for instance, on an Arduino Uno.
If you’re an AVR coder, or interested in direct-digital synthesis or PWM audio output, you should have a look at his code (zip file). If you’d just like to use the chip to make some tunes, have a gander at the video below the break.
It’s pretty sweet to get six channels of 31.25 kHz sampled 8-bit audio running on a 16MHz chip. The code underlying it works through some tricky optimization in the sample update routine (UpdateVoiceSample() in play.c if you’re reading along) and by carefully prioritizing the time critical elements.
For instance, the pitch is updated once every two PWM samples, I/O and other auxiliary player tasks every eights samples, and the sound’s dynamic volume envelope is only recalculated every 48 samples. Doing the slow math as infrequently as possible lets [Erix] make his timing.
And to round out the tools, [Erix] also provides wavetable editors and song generators in Lua to compile the tables of music data that the AVR routines need to run.
If you’re not impressed by this bit of AVR C coding, then you’ve not tried to implement something similar yourself.