An envelope follower is a circuit or algorithm that tracks the slowly varying amplitude of an input signal — its envelope — and outputs that amplitude as a separate, usable control signal without altering the input. Parameters: (1) detection — conversion of instantaneous signal level into a unipolar level (precision rectification, squaring, or magnitude computation); (2) time constants — attack (rise) and release (fall) smoothing that decide which level variations are tracked and which are averaged out; (3) output form — a voltage, digital value, or control signal with a defined gain relation to the measured level. The follower is a derivation stage: it produces a second signal about the first. Persistence mechanism: realized as an analog block (precision rectifier followed by RC low-pass smoothing) and a digital block (one-pole smoothing on rectified magnitude), standardized as the level-detection primitive in every automatic gain control, compressor, limiter, sidechain processor, and peak meter; the pattern persists through circuit-design textbooks and DSP code libraries that reproduce the rectify–smooth structure across generations of hardware and software. [formal: secutor | substrate: matter | horizon: generations | explicit: yes | epoch: 0.01]
Accepted ontology entry
envelope-follower
An envelope follower is a circuit or algorithm that tracks the slowly varying amplitude of an input signal — its envelope — and outputs that amplitude as a separate, usable control signal without altering the input. Parameters: (1) detecti…
Definition
Why it is in scope
A human-made signal-analysis block built to persist as the standard level-detection primitive inside dynamic audio processing.
Names and aliases
- envelope-followeren · CANONICAL
Relations from this entry
- compressorSERVES →
Envelope follower is built and maintained for the sake of dynamics control in compressors: it tracks the amplitude envelope and provides the control signal that drives gain reduction. The follower exists to serve the compressor's designed purpose of level control. Servant points at master per Law 8d.
- audio-processingINSTANCE_OF →
Envelope follower is a specific signal-analysis block used within audio processing: it tracks slowly varying amplitude and outputs a control signal for dynamics, gating, and modulation. A competent speaker classifies it as a kind of audio processing operation. Nearest kind per Law 11e; ladder does not already derive this rung.
Relations to this entry
- noise-gate← DEPENDS_ON
Level detection: a noise-gate must track signal amplitude to decide when it opens or closes. The envelope follower is the operational mechanism for this — it produces the control signal tracking input level. Remove the envelope follower and the gate cannot detect signal level, so it stops operating. Law 8 removal test passes. Direction: noise-gate (dependent) → envelope-follower (mechanism).
- compressor← DEPENDS_ON
A compressor needs an envelope follower to operate now: the envelope follower tracks the amplitude envelope of the input signal and drives the gain-reduction control voltage. Remove the envelope follower and the compressor has no means to map input level to gain reduction — its core dynamic control ceases. Present-tense removal test per Law 8.
- expander← DEPENDS_ON
Level detection: an expander continuously compares input level to a threshold to decide how much to expand. The envelope follower is the mechanism for real-time amplitude tracking — it produces the control signal the expander depends on. Remove it and the expander has no level-detection, so it stops operating. Law 8 removal test passes. Direction: expander (dependent) → envelope-follower (mechanism).
Record identity
- Created
- Sep 20, 2026, 3:32 PM UTC
- Content hash
- f6b721980fe0efdd83c2f6be16c288751090a099f0585610273a6dfbcf13e503