912 envelope follower

moog912 · modulation

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; gate — acts while the level is high (reacts to both edges)

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. ⚠ The GATE's detection level is a FIXED constant that does not scale with this knob, so SENS alone decides how loud the input must be to open it — and below about 0.157 nothing can: the level required passes full scale, so the bottom sixth of this dial cannot open the GATE output on any signal at all, however loud (#1914). The ENV output keeps working there; it is only the gate that goes unreachable. The faceplate prints the required input level in dBFS, and a dash once it becomes impossible.
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). ⚠ The dial is a bare 0..1 but the thing it sets is a frequency, and the mapping is INVERTED and logarithmic: 50 Hz at 0, 1 Hz at 1 — a 5.6-octave span in which turning the knob UP makes the number go DOWN. The factory setting of 0.5 is 7.07 Hz, which neither the knob nor its label can tell you, so the faceplate prints it.

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. ⚠ The GATE's detection level is a FIXED constant that does not scale with this knob, so SENS alone decides how loud the input must be to open it — and below about 0.157 nothing can: the level required passes full scale, so the bottom sixth of this dial cannot open the GATE output on any signal at all, however loud (#1914). The ENV output keeps working there; it is only the gate that goes unreachable. The faceplate prints the required input level in dBFS, and a dash once it becomes impossible.

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). ⚠ The dial is a bare 0..1 but the thing it sets is a frequency, and the mapping is INVERTED and logarithmic: 50 Hz at 0, 1 Hz at 1 — a 5.6-octave span in which turning the knob UP makes the number go DOWN. The factory setting of 0.5 is 7.07 Hz, which neither the knob nor its label can tell you, so the faceplate prints it.

source

moog912.ts on GitHub.