Swapping the FFT index driving a visual parameter aligns the visual energy with the new section's audio driver

The reactivity re-point transition is triggered when a section change shifts which frequency band carries the energy — for example a bass-led main section moving to a highs-led breakdown. The FFT index in the visual parameter’s reactive thunk is swapped from one bin to another (e.g. a.fft[0] to a.fft[3]) so the visual motion tracks the new dominant energy region. This maintains AV coherence: audio and visual keep agreeing on where the energy is. Only four bins are available (a.fft[0..3] = bass/low-mid/high-mid/highs); onset-, tempo-, and RMS-driven transitions are not possible and must not be authored.

Examples

.modulateRotate(osc(2), () => a.fft[3] * 2) switches the rotation driver from bass to highs for a breakdown, so the visual motion thins with the highs leading rather than pumping with the kick.

Assessment

What is AV coherence, and how does reactivity re-pointing maintain it across a section change? Name the four available FFT bins and the ranges they cover.