Filters
If oscillators are the vocal cords of a synth, the filter is the mouth. It doesn't create sound, it sculpts what the oscillator gives it by removing harmonics. This is why classic synthesis is called subtractive: start rich, carve away.
The two controls that matter:
- Cutoff: the frequency where the filter starts removing content. On a low-pass filter, everything above the cutoff is shaved off. Cutoff is effectively a brightness knob.
- Resonance: a boost right at the cutoff point. A little adds presence; a lot makes the filter sing at its own frequency, the classic squelchy acid sound.
Below, a bright sawtooth drone runs through a filter. Watch the spectrum while you sweep Cutoff , you can literally see the harmonics being erased. Then raise Reso and sweep again.
Try this: switch to HP (high-pass) and sweep cutoff up, now the lows vanish and the sound turns thin and tinny, like a phone speaker. BP (band-pass) keeps only a slice around the cutoff. Every EQ, wah pedal, and DJ filter you've ever heard is one of these three.
Checkpoint
Play both filter sweeps. Which one has high resonance?