A rising audio energy arc can be mapped to rising visual motion rate or scale so that both domains accelerate together during a build

By summing all four FFT bands (a.fft[0]+a.fft[1]+a.fft[2]+a.fft[3]) into an energy scalar E, a Hydra sketch can drive global speed or scale proportionally to overall audio energy. As a build-up raises the mix level, E rises and the visual accelerates/grows correspondingly. This is an energy ramp, not a beat-locked accelerando — the visual speeds up with loudness, not in per-beat steps. The coupling survives silence (E→0) and is realizable in the browser without any feature beyond the 4-bin shim. It directly implements the AV structural analogy X3: audio build-up / density-curve ≙ visual speed/scale.

Examples

let E = ()=>(a.fft[0]+a.fft[1]+a.fft[2]+a.fft[3])
osc(10,0.1,1).rotate(()=>0.1+E()*0.4).scale(()=>1+E()*0.3).out()

During a build the image rotates faster and zooms larger; at silence it settles to a slow small baseline.

Assessment

Design a Hydra sketch for a build that goes from sparse to dense over 8 bars. Explain which bands to sum, what visual parameters to drive, and why this is an energy ramp rather than a beat-locked acceleration.