follow — Envelope follower unit generator.


Envelope follower unit generator.


ares follow asig, idt


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 )


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


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

Example 370. Example of the follow opcode.

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

; 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

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

instr 1

asig soundin "drumsMlp.wav"
     outs asig, asig


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

;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

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


Author: Paris Smaragdis
MIT, Cambridge