The Alternative Csound Reference Manual
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# reverb

reverb -- Reverberates an input signal with a "natural room" frequency response.

## Description

Reverberates an input signal with a "natural room" frequency response.

## Syntax

ar reverb asig, krvt [, iskip]

## Initialization

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

## Performance

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.

## Examples

Here is an example of the reverb opcode. It uses the files reverb.orc and reverb.sco.

Example 1. Example of the reverb opcode.

    /* reverb.orc */
    ; 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
    endin

    ; (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
    endin
    /* reverb.orc */

    /* reverb.sco */
    ; 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
    e
    /* reverb.sco */

## See Also

alpass, comb, valpass, vcomb

## Credits

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

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