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Toot 9: Global Stereo Reverb

In the previous example you may have noticed the soundin source being "cut off" at ends of notes, because the reverb was inside the instrument itself. It is better to create a companion instrument, a global reverb instrument, to which the source signal can be sent. Let's also make this stereo.

Variables are named cells which store numbers. In Csound, they can be either local or global, are available continuously, and can be updated at one of four rates - setup, i-rate, k-rate, or a-rate.

Local Variables (which begin with the letters p, i, k, or a) are private to a particular instrument. They cannot be read from, or written to, by any other instrument.

Global Variables are cells which are accessible by all instruments. Three of the same four variable types are supported (i, k, and a), but these letters are preceded by the letter g to identify them as "global." Global variables are used for "broadcasting" general values, for communicating between instruments, and for sending sound from one instrument to another.

The reverb instr99 below receives input from instr9 via the global a-rate variable garvbsig. Since instr9 adds into this global, several copies of instr9 can do this without losing any data. The addition requires garvbsig to be cleared before each k-rate pass through any active instruments. This is accomplished first with an init statement in the orchestra header, giving the reverb instrument a higher number than any other (instruments are performed in numerical order), and then clearing garvbsig within instr99 once its data has been placed into the reverb.

  sr        =    18900          ; toot9.orc
  kr        =    945
  ksmps     =    20
  nchnls    =    2              ; stereo
  garvbsig  init 0              ; make zero at orch init time

  instr 9
     idur        =    p3
     iamp        =    p4
     iskiptime   =    p5   
     iattack     =    p6
     irelease    =    p7
     ibalance    =    p8   ; panning: 1=left, .5=center, 0=right
     irvbgain    =    p9                  
     kamp        linen      iamp, iattack, idur, irelease  
     asig        soundin   "soundin.aiff", iskiptime
     arampsig    =         kamp * asig            
                 outs      arampsig * ibalance,  arampsig * (1 - ibalance)
     garvbsig    =         garvbsig + arampsig * irvbgain  

  instr 99                 ; global reverb
     irvbtime    =         p4 
     asig        reverb    garvbsig,  irvbtime ; put global signal into reverb
            outs asig, asig 
     garvbsig    =    0              ; then clear it

In the score we turn the global reverb on at time 0 and keep it on until irvbtime after the last note.

; ins     strt dur  rvbtime                  ; toot9.sco
  i99     0    9.85 2.6

; ins strt dur  amp  skip atk  rel  balance(0-1) rvbsend
   i9 0    1    .5   0    .02  .1   1            .2
   i9 2    2    .5   0    .03  .1   0            .3
   i9 3.5  2.25 .5   0    .9   .1   .5           .1
   i9 4.5  2.25 .5   0    1.2  .1   0            .2
   i9 5    2.25 .5   0    .2   .1   1            .3

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