Filters: types, cutoff, resonance, and rolloff

The filter is the single most-touched control in subtractive synthesis and in a live-coded set alike: whether you are carving a techno bassline in SuperCollider, keeping a dub chord from fighting the sub, or riding a cutoff sweep as the one gesture the crowd can hear evolving, everything hinges on knowing what a filter will do before you turn the knob. This module builds toward exactly that fluency — one raw sawtooth, four deliberately different sonic outcomes, each justified in terms of type, cutoff, Q, and slope.

The arc starts fully supported. You first internalise the map — the idea that a filter selectively attenuates frequency ranges, and the basic response shapes — then anchor the vocabulary that makes settings predictable rather than guessed: the half-power (−3 dB) definition of cutoff, Q and its reciprocal rq, and the 6 dB-per-octave-per-pole rule for slope. Guided exercises then pull in the procedural atoms as just-in-time how-to pointers: murking a bright oscillator into a low-end bass with a mid-cutoff LPF, tightening sub-bass with a highpass below ~40 Hz, and thinning a chord into an airy voice by highpassing instead of lowpassing. Extreme resonance behaviour (self-oscillation) and keytracking close the set, so that by the capstone you patch all four targets unassisted.

Every required atom gates a capstone deliverable — you cannot describe the whistling tone without self-oscillation, nor the airy chord voice without knowing when to reach for a highpass, nor the timbre-preserving patch without keytrack. Supporting atoms deepen the picture: Surge XT’s filter configurations, offset mode, and scene highpass give a concrete rig to practise in, while ladder topology and the resonance-edge patch show where character and expressivity live beyond the numbers. The two bread-and-butter procedures — LPF bass definition and sub-bass highpassing — recur in nearly every session, so drill them inside real patches until they are automatic.

Runnable examples

Generated from the context/ instrument corpus by concept (redistributable idioms only). Do not edit — regenerate with gen-module-examples.mjs.

resonant-filter

SinOsc s => LPF f => dac; 400 => f.freq;

_{chuck-0002 · MIT}

play :e2, cutoff: 90, res: 0.9, release: 0.3

_{sonicpi-0022 · CC0}

sub-bass

osc 27.5 >> audio

_{punctual-0002 · CC0-1.0}

synth :subpulse, note: :e1, sustain: 0.4, amp: 1.4

_{sonicpi-0016 · CC0}