Audio Reactive Scale

Layer scale pulses with the music using converted audio keyframes.

Expression Code

// Audio Reactive Scale
// Apply to Scale
// First: select your audio layer, then Animation > Keyframe Assistant >
// Convert Audio to Keyframes. This creates a layer called "Audio Amplitude".

audio = thisComp.layer("Audio Amplitude").effect("Both Channels")("Slider");
minScale = 90;     // Scale % during silence
maxScale = 130;    // Scale % at the loudest point
maxAmp = 25;       // Amplitude treated as "loudest" — check your keyframed values
smoothness = 0.05; // Smoothing window in seconds (0 = raw and jittery)

if (smoothness > 0) {
  amp = audio.smooth(smoothness, 5);
} else {
  amp = audio.value;
}
s = linear(amp, 0, maxAmp, minScale, maxScale);
res = (value.length == 3) ? [s, s, s] : [s, s];
res;

Select your music layer and run Animation > Keyframe Assistant > Convert Audio to Keyframes — AE creates a null called "Audio Amplitude" with baked amplitude sliders. Apply this to Scale on any layer (2D or 3D — the expression matches the dimensions automatically). Scrub to the loudest section, check the "Both Channels" slider value there, and set maxAmp to roughly that number so peaks hit maxScale exactly. The smooth() call removes per-frame jitter so the pulse feels musical rather than twitchy. If you later swap the music and re-convert, delete the old Audio Amplitude null first — otherwise AE names the new one "Audio Amplitude 2" and this expression keeps reading the stale keyframes.

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