Hello,

In the comb opcode examples, an additional instrument is made separately for 
the reverb. Below is an archive .csd with the manual example written. What I 
dont understand is why after using "comb", whe have to reset the global 
variable "gamix" to 0, since in the next pass it is assigned again with the 
same gamix = a1? Why one initialization and no reset don´t work?

Thanks in advance,
Robson





-o comb.wav





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

; Initialize the audio mixer.
gamix init 0

; Instrument #1.
instr 1
  ; Generate a source signal.
  a1 oscili 30000, cpspch(p4), 1
  ; Output the direct sound.
  out a1

  ; Add the source signal to the audio mixer.
  gamix = a1
endin

; Instrument #99 (highest instr number executed last)
instr 99
  krvt = 1.5
  ilpt = 0.1

  ; Comb-filter the mixed signal.
  a99 comb gamix, krvt, ilpt
  ; Output the result.
  out a99

  ; Empty the mixer for the next pass.
  gamix = 0
endin





; 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=7.00
i 1 0 0.1 7.00
; Play Instrument #1 for a tenth of a second, p4=7.02
i 1 1 0.1 7.02
; Play Instrument #1 for a tenth of a second, p4=7.04
i 1 2 0.1 7.04
; Play Instrument #1 for a tenth of a second, p4=7.06
i 1 3 0.1 7.06

; Make sure the comb-filter remains active.
i 99 0 5
e




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But exactly as it is written here (i.e. gamix=a1 withou adding) it works 
only if at the end we have gamix=0. If there is no gamix = 0 then there are 
samples out of range. Another example, if comb is in the same instument, 
i.e.,

instr 1
  krvt = 1.5
  ilpt = 0.1
  a1 oscili 30000, 440, 1
  a99 comb a1, krvt, ilpt
  out a1+a99
endin

then the in-signal is repeated only once, i.e. just one echo. So if we dont 
have gamix=0 there is too much strange reverberation, and if it is in the 
same instrument there is too little reverb.

It seems like a strange need in the inner workings of k-pass to have gamix 
reassigned to a1 and to 0 alternately in different instruments, anh?

>From: Istvan Varga 
>Reply-To: csound@lists.bath.ac.uk
>To: csound@lists.bath.ac.uk
>Subject: Re: [Csnd] resetting in comb opcode
>Date: Thu, 12 Jan 2006 18:39:41 +0100
>
>On Thursday 12 January 2006 18:33, Robson Cozendey wrote:
> > Hello,
> >
> > In the comb opcode examples, an additional instrument is made separately 
>for
> > the reverb. Below is an archive .csd with the manual example written. 
>What I
> > dont understand is why after using "comb", whe have to reset the global
> > variable "gamix" to 0, since in the next pass it is assigned again with 
>the
> > same gamix = a1?
>
>That should probably be gamix = gamix + a1 (or vincr gamix, a1), so that
>with multiple instances of instr 1 the output is mixed. Then, with
>accumulating the output, it should really be reset to zero.
>--
>Send bugs reports to this list.
>To unsubscribe, send email to csound-unsubscribe@lists.bath.ac.uk

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Thanks Istvan!
I think now I understood


>From: Istvan Varga 
>Reply-To: csound@lists.bath.ac.uk
>To: csound@lists.bath.ac.uk
>Subject: Re: [Csnd] resetting in comb opcode
>Date: Thu, 12 Jan 2006 19:21:11 +0100
>
>On Thursday 12 January 2006 19:12, Robson Cozendey wrote:
>
> > But exactly as it is written here (i.e. gamix=a1 withou adding) it works
> > only if at the end we have gamix=0. If there is no gamix = 0 then there 
>are
> > samples out of range.
>
>Yes, you do in fact need to reset even with the original example,
>as otherwise the last output would be repeated when instr 1 is not
>active. However, in general, you should both add and reset.
>
> > Another example, if comb is in the same instument,
> > i.e.,
> >
> > instr 1
> >   krvt = 1.5
> >   ilpt = 0.1
> >   a1 oscili 30000, 440, 1
> >   a99 comb a1, krvt, ilpt
> >   out a1+a99
> > endin
> >
> > then the in-signal is repeated only once, i.e. just one echo. So if we 
>dont
> > have gamix=0 there is too much strange reverberation, and if it is in 
>the
> > same instrument there is too little reverb.
>
>That is because instr 1 is turned off before you could get more
>reverberation. That is why there is a separate instrument that is
>always on.
>--
>Send bugs reports to this list.
>To unsubscribe, send email to csound-unsubscribe@lists.bath.ac.uk

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