follow
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## follow

follow — Envelope follower unit generator.

## Description

Envelope follower unit generator.

## Syntax

    ares follow asig, idt

## Initialization

idt -- This is the period, in seconds, that the average amplitude of asig is reported. If the frequency of asig is low then idt must be large (more than half the period of asig )

## Performance

asig -- This is the signal from which to extract the envelope.

## Examples

Here is an example of the follow opcode. It uses the file follow.csd, and beats.wav.

Example 339. Example of the follow opcode.

See the sections Real-time Audio and Command Line Flags for more information on using command line flags.

    <CsoundSynthesizer>
    <CsOptions>
    ; Select audio/midi flags here according to platform
    -odac      ;;;realtime audio out
    ;-iadc    ;;;uncomment -iadc if realtime audio input is needed too
    ; For Non-realtime ouput leave only the line below:
    ; -o follow.wav -W ;;; for file output any platform
    </CsOptions>
    <CsInstruments>

    sr = 44100
    ksmps = 32
    nchnls = 2
    0dbfs  = 1

    instr 1

    asig soundin "beats.wav"
         outs asig, asig

    endin

    instr 2	;envelope follower

    as   soundin "beats.wav"
    as   = as*.7		;reduce volume a bit
    at   tone    as, 500	;smooth estimated envelope
    af   follow  at, p4
    asin poscil3 .5, 440, 1
    ; "beats.wav" provides amplitude for poscil
    asig balance asin, af
         outs    asig, asig

    endin
    </CsInstruments>
    <CsScore>
    ;sine wave.
    f 1 0 32768 10 1

    i 1 0 2
    i 2 2 2 0.001 ;follow quickly
    i 2 5 3 0.2   ;follow slowly
    e
    </CsScore>
    </CsoundSynthesizer>

To avoid zipper noise, by discontinuities produced from complex envelope tracking, a lowpass filter could be used, to smooth the estimated envelope.

## Credits

Author: Paris Smaragdis
MIT, Cambridge
1995

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