@maruaudio/dsp/dynamics/envelope-follower tracks the level of a signal with a branching one-pole detector: s = c·s + (1 − c)·t, where t is |x| (peak) or x² (RMS) and c is the attack coefficient when t rises above the state, the release coefficient otherwise. Coefficients are exp(−1 / (seconds · rate)), rounded to f32, as is the detector state. RMS mode returns sqrt(s). The leaf also exports a standalone mean-square window for compressor detectors.

const state = initEnvelopeFollower(48000)
setEnvelopeFollowerAttack(state, 0.005)
const level = envelopeFollowerTick(state, x)

Parameters

envelopeTimeCoefficient(seconds, rate) clamps seconds to 0.0001 to 10 and the rate to 8000 to 384000 Hz. rmsWindowCoefficient clamps seconds to 0.0005 to 0.2; rmsMeanSquareTick(state, x, c) returns the new f32 mean square and leaves the square root to the caller.

Lifecycle

initEnvelopeFollower(sampleRate) → setters → envelopeFollowerTick → resetEnvelopeFollower, which zeroes the detector and keeps the settings. prepareEnvelopeFollowerSampleRate re-derives both coefficients from the stored times without allocating. The mean-square helpers are stateless; the caller owns their state.

When to use it

A control signal from an audio input: ducking, an auto-wah, a gate or meter detector. Use the separate mean-square window when the averaging interval must be independent of the attack and release.

Limits

• Mono sample tick. In RMS mode the same coefficients both average the square and shape the envelope; the standalone window separates those.
• Clamps are the kernel node's conditional clamp, not @maru/math-range.
• audio-kernels keeps the PCM16 render entries and node-parameter ABI.