reverb — Reverberates an input signal with a “natural room” frequency response.


Reverberates an input signal with a “natural room” frequency response.


ares reverb asig, krvt [, iskip]


iskip (optional, default=0) -- initial disposition of delay-loop data space (cf. reson). The default value is 0.


krvt -- the reverberation time (defined as the time in seconds for a signal to decay to 1/1000, or 60dB down from its original amplitude).

A standard reverb unit is composed of four comb filters in parallel followed by two alpass units in series. Loop times are set for optimal “natural room response.” Core storage requirements for this unit are proportional only to the sampling rate, each unit requiring approximately 3K words for every 10KC. The comb, alpass, delay, tone and other Csound units provide the means for experimenting with alternate reverberator designs.

Since output from the standard reverb will begin to appear only after 1/20 second or so of delay, and often with less than three-fourths of the original power, it is normal to output both the source and the reverberated signal. If krvt is inadvertently set to a non-positive number, krvt will be reset automatically to 0.01. (New in Csound version 4.07.) Also, since the reverberated sound will persist long after the cessation of source events, it is normal to put reverb in a separate instrument to which sound is passed via a global variable, and to leave that instrument running throughout the performance.


Here is an example of the reverb opcode. It uses the file reverb.csd.

Example 398. Example of the reverb 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
; Audio out   Audio in    No messages
-odac           -iadc     -d     ;;;RT audio I/O
; For Non-realtime ouput leave only the line below:
; -o reverb.wav -W ;;; for file output any platform

; Initialize the global variables.
sr = 44100
kr = 4410
ksmps = 10
nchnls = 1

; init an audio receiver/mixer
ga1 init 0 

; Instrument #1. (there may be many copies)
instr 1 
  ; generate a source signal
  a1 oscili 7000, cpspch(p4), 1 
  ; output the direct sound
  out a1  
  ; and add to audio receiver
  ga1 = ga1 + a1 

; (highest instr number executed last)
instr 99 
  ; reverberate whatever is in ga1
  a3 reverb ga1, 1.5
  ; and output the result
  out a3 
  ; empty the receiver for the next pass
  ga1 = 0 


; Table #1, a sine wave.
f 1 0 128 10 1

; p4 = frequency (in a pitch-class)
; Play Instrument #1 for a tenth of a second, p4=6.00
i 1 0 0.1 6.00
; Play Instrument #1 for a tenth of a second, p4=6.02
i 1 1 0.1 6.02
; Play Instrument #1 for a tenth of a second, p4=6.04
i 1 2 0.1 6.04
; Play Instrument #1 for a tenth of a second, p4=6.06
i 1 3 0.1 6.06

; Make sure the reverb remains active.
i 99 0 6


See Also

alpass, comb, valpass, vcomb


Author: William “Pete” Moss
University of Texas at Austin
Austin, Texas USA
January 2002