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vcomb

Variably reverberates an input signal with a “colored” frequency response.

Syntax

ares = vcomb(asig, krvt, xlpt, imaxlpt [, iskip] [, insmps])

ares vcomb asig, krvt, xlpt, imaxlpt [, iskip] [, insmps]

Initialization

imaxlpt -- maximum loop time for klpt

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

insmps (optional, default=0) -- delay amount, as a number of samples.

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).

xlpt -- variable loop time in seconds, same as ilpt in comb. Loop time can be as large as imaxlpt.

This filter reiterates input with an echo density determined by loop time xlpt. The attenuation rate is independent and is determined by 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). Output will appear only after ilpt seconds.

Examples

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

Example of the vcomb opcode.
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<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
; Audio out   Audio in
-odac           -iadc       -M0 ;;;RT audio I/O with MIDI in
</CsOptions>
<CsInstruments>

; Example by Jonathan Murphy and Charles Gran 2007
  sr        =  44100
  ksmps     =  10
  nchnls    =  2

        ; new, and important. Make sure that midi note events are only
        ; received by instruments that actually need them.

        ; turn default midi routing off
        massign         0, 0
        ; route note events on channel 1 to instr 1
        massign         1, 1

; Define your midi controllers
#define C1 #21#
#define C2 #22#
#define C3 #23#

; Initialize MIDI controllers
            initc7    1, $C1, 0.5                 ;delay send
            initc7    1, $C2, 0.5                 ;delay: time to zero
            initc7    1, $C3, 0.5                 ;delay: rate 

  gaosc     init      0

; Define an opcode to "smooth" the MIDI controller signal
    opcode smooth, k, k
  kin       xin
  kport     linseg    0, 0.0001, 0.01, 1, 0.01
  kin       portk     kin, kport
            xout      kin
    endop

instr   1  
 ; Generate a sine wave at the frequency of the MIDI note that triggered the intrument
  ifqc      cpsmidi
  iamp      ampmidi   10000
  aenv      linenr    iamp, .01, .1, .01          ;envelope
  a1        oscil     aenv, ifqc, 1
; All sound goes to the global variable gaosc
  gaosc     =  gaosc + a1
    endin

    instr     198 ; ECHO
  kcmbsnd   ctrl7     1, $C1, 0, 1                ;delay send
  ktime     ctrl7     1, $C2, 0.01, 6             ;time loop fades out
  kloop     ctrl7     1, $C3, 0.01, 1             ;loop speed
; Receive MIDI controller values and then smooth them
  kcmbsnd   smooth    kcmbsnd
  ktime     smooth    ktime
  kloop     smooth    kloop
  imaxlpt   =  1                                  ;max loop time
; Create a variable reverberation (delay) of the gaosc signal
  acomb     vcomb     gaosc, ktime, kloop, imaxlpt, 1
  aout      =  (acomb * kcmbsnd) + gaosc * (1 - kcmbsnd)
            outs      aout, aout
  gaosc     =  0
    endin

</CsInstruments>

<CsScore>
f1 0 16384 10 1
i198 0 10000
e
</CsScore>
</CsoundSynthesizer>

See also

Reverberation

Credits

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