912 envelope follower

moog912 · modulation · schema v1

912 Envelope Follower (moogafakkin System 55 clone — categorized under Ports -> moogafakkin). Tracks the amplitude envelope of an audio input and outputs it as a control voltage, plus a gate when the envelope is above threshold. SENSITIVITY sets the input drive; SMOOTHING sets how fast the envelope tracks (envelope-detector lowpass). Pure Web Audio (rectify -> lowpass -> CV; threshold -> gate). Beige moogafakkin faceplate (the intrinsic always-on look shared by the moogafakkin module family).

A clean-room recreation of the Moog 912 Envelope Follower — a passive ANALYSIS utility that listens to an incoming audio signal's loudness and turns it into a smooth control voltage (an 'envelope') plus a gate that's high while the input is sounding. Internally the audio is full-wave rectified (|x|, turning the bipolar waveform into a magnitude) and lowpass-filtered into a slowly-varying level; a steep threshold on that level produces the gate. Patch a drum loop, vocal, or any live source in, and use ENV to open a VCA/filter that tracks the input's dynamics, or GATE to fire an envelope generator from an external sound. Mental model: 'how loud is this right now?' as a CV, plus a 'is it playing?' on/off gate. The two knobs trade off how hard the signal is measured (SENS) and how lazily the envelope reacts (SMOOTH).

the faceplate

1 inputs · 2 outputs · 2 params

about this module

Hover a control, or open the patch panel and hover a jack.

inputs

id	cable	what it does
`audio`	audio	The signal to follow — the audio being measured (not a modulator). Its amplitude drives both the ENV and GATE outputs; louder material gives a bigger envelope. Patch a drum, vocal, or full mix here. audio signal

outputs

id	cable	what it does
`env`	cv	The smoothed amplitude envelope as a control voltage: the rectified, lowpass-filtered loudness of the input. Patch it into a VCA's gain or a filter's cutoff to make them track how loud the source is. control voltage (CV)
`gate`	gate	Goes high (~1) while the followed envelope is above the detection threshold (the input is audibly playing) and low (~0) when it falls quiet — an auto-gate derived from the sound itself. Patch it into an envelope generator or VCA to trigger from a live source. gate / trigger

params

id	label	range	default	curve
`sensitivity`	Sens	0..1	0.7	linear
`smoothing`	Smooth	0..1	0.5	linear

controls

control	what it does
Sens	Input gain into the follower — how hard the incoming signal hits the detector. Higher SENS makes quiet material produce a bigger envelope (and opens the gate more readily); lower SENS only responds to loud peaks.
Smooth	How lazily the envelope reacts: more SMOOTH lowers the detector's lowpass cutoff so the CV glides slowly and ignores fast transients (a smooth contour); less SMOOTH speeds it up so the envelope snaps to each peak (a punchy, percussive follow).

source

moog912.ts on GitHub.