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follow

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 drumsMlp.wav.

Example of the follow opcode.
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<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 "drumsMlp.wav"
     outs asig, asig

endin

instr 2 ;envelope follower

as   soundin "drumsMlp.wav"
as   = as*.7            ;reduce volume a bit
at   tone    as, 500    ;smooth estimated envelope
af   follow  at, p4
asin poscil3 .5, 440, 1
; "drumsMlp.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.

See also

Sensing and Control: Envelope followers

Credits

Author: Paris Smaragdis
MIT, Cambridge
1995