Mapping high-mid band to rotation speed or line thickness gives geometric visuals a crisp, articulate audio response

Among the 4-bin FFT bands, the high-mid (a.fft[2]) corresponds to percussive attack elements, synth articulation, and melodic presence — the most ‘crisp’ and defined part of the frequency spectrum. For geometric visuals, whose aesthetic is precision and articulation, driving rotation speed or line thickness from this band produces a response that matches the style: sharp, defined, not muddy. Bass (a.fft[0]) would feel too heavy and rhythmically dominant; highs (a.fft[3]) would feel noisy and frenetic. The design principle is to match the reactive band’s sonic character to the visual style’s character. All reactivity is envelope-following only — no beat-locking is available.

Examples

Hydra: .rotate(()=>speed + a.fft[2]*0.3) — rotation articulates with the mid-range melodic content, giving a precision feel. Alternatively, stroke width in GLSL: float w = baseW + a.fft[2]*0.02.

Assessment

A geometric patch uses bass (a.fft[0]) for rotation speed. The instructor says to use high-mid instead. Explain the reasoning in terms of sonic character matching visual style. What does ‘envelope-following only’ mean for the type of visual motion this produces?