What sound actually *is*, and why the sawtooth is the acid oscillator.
Three properties of any sound. Press power on, then hold note and play:
Harmonics are the secret. Any repeating wave is secretly a stack of pure sine waves (the fundamental at the pitch you hear, plus overtones at 2×, 3×, 4×… that frequency). The right-hand spectrum shows them as spikes. Switch waveforms and watch:
| wave | harmonics present | sound | spectrum |
|---|---|---|---|
| sine | fundamental only | pure, hollow, "flute-y" | one lone spike |
| triangle | odd only, fall off fast (1/n²) | soft, mellow | few small spikes |
| square | odd only (1/n) | hollow, buzzy, "8-bit" | tall odd spikes |
| sawtooth | all harmonics (1/n) | bright, brassy, rich | full comb of spikes |
Why saw = acid. The TB-303's oscillator is basically just saw or square. A synth subtracts: you start with the most harmonically-rich source and carve it with a filter. The sawtooth has the most harmonics to carve, so it gives the filter the most to "bite" into — that's why sweeping a filter over a saw makes that liquid, vocal, squelchy acid sound. Next lesson (01) we shape it in time with an envelope; then Module 1 adds the filter and it starts to sound like acid.
Note: these built-in oscillators are band-limited (anti-aliased), so the spectrum stops cleanly below the Nyquist limit instead of folding back as garbage — a nicety Web Audio handles for us.