[sdiy] In praise of the ATM STM32F303

[Olivier Gillet]

> Do it using the same method as the original string machines. We have 12 oscillators tuned to the top octave. Twelve NCO updates doesn't take long to do. The oscillators drive binary counters, which then provide all the different octaves you need in their various bits.
> In order to provide output waveforms, you shape the square-wave outputs from the counter bits using a one-pole IIR filter. This simulates simple RC filtering and gives you somewhere between a triangle wave and a  "shark's fin", depending on your filter coefficient. It *must* be quicker to calculate a IIR filter than do a PolyBLEP.

At which sample rate would this run?

You would need the frequency of your top NCOs to be equal to fs/N,
where N is an integer, if you don't want to deal with aliasing issues.

If this is not the case, you'd need a band-limiting scheme not only
for the NCO but also for all the divided octaves - since their
transitions do not fall exactly on edges.