An exp-curve bass amplitude pump is the supported proxy for a kick-keyed visual sidechain, and it is not the same thing

A true kick-keyed visual sidechain would duck the visual specifically on each kick onset, using a per-instrument signal. This is not achievable: the 4-bin FFT is a full-mix energy reading; the kick cannot be isolated. The supported substitute is an amplitude pump on the bass band with an exp curve: scale(()=>1+a.fft[0]*a.fft[0]*g). This produces a ‘duck/pump on loud bass’ feel and is realizable now. The key differences: (1) it pumps on any loud bass, not only kicks; (2) it stays elevated during sustained bass, not just the transient; (3) it never ducks — it inflates on loud hits. Mislabeling this as a sidechain overstates what the rig delivers.

Examples

src(o0).modulateScale(osc(6),()=>a.fft[0]*a.fft[0]*1.2) pumps on bass energy. During a passage with a bass synth but no kick, it still pumps. During a kick-only pattern, it reacts to the kick — but only because the kick is also the dominant bass energy.

Assessment

Describe what ‘kick-keyed sidechain’ means in audio terms, then explain why the amplitude-pump proxy (a.fft[0]²) is not the same. Name two musical situations where the two would behave differently.