Envelope follower
From Wikipedia, the free encyclopedia
An envelope follower is an electronic circuit used in musical environments to detect the amplitude variations of an incoming sound and to produce a control signal that resembles those variations.
Most practical envelope followers use either half-wave or full-wave rectification of the signal to convert the AC audio input into a pulsed DC signal. Filtering is then used to smooth the final result. This filtering is rarely perfect and some "ripple" is likely to remain on the envelope follower output, particularly for low frequency inputs such as notes from a bass guitar. More filtering gives a smoother result, but decreases the responsiveness of the design, so real-world solutions are a compromise.
Envelope followers are often a component of other circuits, such as a compressor or an auto-wah or envelope-followed filter. In these circuits, the envelope follower is part of what is known as the "side chain", a circuit which describes some characteristic of the input, in this case its volume.
Both expanders and compressors use the envelope's output voltage to control of the gain of an amplifier. Auto-wah uses the voltage to control the cutoff frequency of a filter. The voltage-controlled filter of an analog synthesizer is a similar circuit.
Modern envelope followers can be implemented:
An example of a modern implementation of an envelope follower is the ToadWorks Enveloope.
