Low-pass cutoff + resonance

▸What it is

A low-pass filter lets low frequencies through and gradually cuts everything above a chosen cutoff frequency. Two knobs do most of the work: cutoff (where the filter starts removing brightness) and resonance (how much the filter emphasizes the frequencies right at the cutoff before falling off). Sweep the cutoff down on a saw wave and it goes from bright to muffled; push resonance up and the cutoff frequency itself starts to ring, eventually whistling or even self-oscillating. The filter is where most of the *feel* of a subtractive synth lives — it is the wah, the snap, the breath, the growl, depending on what is moving it.

▸Questions

• What is the difference between a 12 dB and 24 dB filter?

  Both are low-pass; the number is how steeply the filter cuts above the cutoff. 24 dB per octave is the classic "fat" Moog-style sound; 12 dB is gentler and lets more brightness through.

• Why does high resonance make my synth scream?

  Resonance boosts a narrow band right at the cutoff. Crank it and that band becomes loud enough to dominate the signal — eventually the filter is generating its own sine wave at the cutoff frequency.

• Should I automate cutoff or use the filter envelope?

  Both are common. Manual cutoff sweeps are for performance moves; the filter envelope is what makes plucks and basses move on their own with every note.

▸In the curriculum

First taught

BS3 · Open the filter — Sweep the cutoff, add a touch of resonance. Part of the Bass track.

Reused in

The same concept comes back in 6 lessons later in the curriculum, in a new context.

▸Related concepts

Concepts that share a lesson with low-pass cutoff + resonance: