[sdiy] BLIT/BLEP virtual analogue synthesis

[Olivier Gillet]

Hi,

I've already played with these techniques, but in the software world.
I toyed a bit with the idea of doing this on an AVR for the Shruthi,
but this is the kind of things that can quickly get extremely costly -
over the simpler method of generating band-limited wavetables for
saw/square and crossfading between them, Korg DWGS-style). The major
lesson I got from the paper is that once you have a decent band
limited saw and square, you can move on to other waveforms from it by
integration, difference with a phase-shifted version...

But if you're looking at this for software, these things are a bit
outdated compared to BLEP / polyBLEP anyway.

Now back to your question. A 8kHz square wave has harmonics at 8 kHz,
24 kHz, 40 kHz, etc... If you sample it at 44.1 kHz with a soundcard
with good brickwall filters, you'll see a sine wave at 8kHz. Heck, you
won't be able to hear the difference between a sine and square at
8kHz, unless you have superman's ears. You'll hear the difference
between a sine and a sawtooth if you can hear up to 16 kHz - I don't.

So at those frequency, don't expect to see anything happening besides
sine waves, but this is not really a problem.

Given that BLEP gets more and more expensive as the signal frequency
increases (more tails from bleps active at a given point in time), you
could maybe setup something that progressively degrade to wavetables
of band-limited signals as frequency increases to clear up CPU.

Olivier