ER-301/Envelope Follower

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Applications

  • Extracting envelopes from audio.
  • Slew limiting with separate rates for rising and falling portions of the signal.
  • Filtering out triggers by how close they are to each other.

Description

In a nutshell, the Envelope Follower tries to trace the energy (i.e. amplitude) of the input signal while ignoring fast (typically audio-rate) changes. More accurately, this unit rectifies the input signal so that negative portions are flipped to the positive side and then fed through a special kind of low pass filter that has separate frequency cutoffs (really time-decay constants) for the rising and falling portions of the signal. The benefit of having separate frequency cutoffs is that the envelope can quickly react to onsets (percussive hits, for example) but still yield a nice smooth envelope as the sound dies out.

Parameters

attack

Control Type Has Sub-chain? Sub-chain Parameters Fader Scale
Gain/Bias yes gain (-10 to 10)

bias (0s to 1s)

time in seconds


This sets the decay rate for rising portions of the rectified incoming signal. Short decay rates will track the rectified signal very closely while longer decay rates will smooth out the abrupt changes. Literally, this parameter sets how long it takes for the envelope to catch up to a signal who's amplitude is growing.


release

Control Type Has Sub-chain? Sub-chain Parameters Fader Scale
Gain/Bias yes gain (-10 to 10)

bias (0s to 1s)

time in seconds


This sets the decay rate for falling portions of the rectified incoming signal. Short decay rates will track the rectified signal very closely while longer decay rates will smooth out the abrupt changes. Literally, this parameter sets how long it takes for the envelope to catch up to a signal who's amplitude is shrinking.