Description
Convolution based on a uniformly partitioned overlap-save algorithm. Compared to the convolve opcode, 'pconvolve' has these benefits:
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small delay
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possible to run in real-time for shorter impulse files
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no pre-process analysis pass
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can often render faster than convolve
Initialization
ifilcod -- integer or character-string denoting an impulse response soundfile. multichannel files are supported, the file must have the same sample-rate as the orc. [Note: cvanal files cannot be used!] Keep in mind that longer files require more calculation time [and probably larger partition sizes and more latency]. At current processor speeds, files longer than a few seconds may not render in real-time.
ipartitionsize (optional, defaults to the output buffersize [-b]) -- the size in samples of each partition of the impulse file. This is the parameter that needs tweaking for best performance depending on the impulse file size. Generally, a small size means smaller latency but more computation time. If you specify a value that is not a power-of-2 the opcode will find the next power-of-2 greater and use that as the actual partition size.
ichannel (optional) -- which channel to use from the impulse response data file.
Performance
ain -- input audio signal.
The overall latency of the opcode can be calculated as such [assuming ipartitionsize is a power of 2]
ilatency = (ksmps < ipartitionsize ? ipartitionsize + ksmps : ipartitionsize)/sr
Examples
Instrument 1 shows an example of real-time convolution.
Instrument 2 shows how to do file-based convolution with a 'look ahead' method to remove all delay.
![[Note]](images/note.png)
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NOTE |
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You will need to download the impulse response files from noisevault.com or replace the filenames with your own impulse files |
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sr = 44100
ksmps = 100
nchnls = 2
instr 1
kmix = .5 ; Wet/dry mix. Vary as desired.
kvol = .5*kmix ; Overall volume level of reverb. May need to adjust
; when wet/dry mix is changed, to avoid clipping.
; do some safety checking to make sure we the parameters a good
kmix = (kmix < 0 || kmix > 1 ? .5 : kmix)
kvol = (kvol < 0 ? 0 : .5*kvol*kmix)
; size of each convolution partion -- for best performance, this parameter needs to be tweaked
ipartitionsize = p4
; calculate latency of pconvolve opcode
idel = (ksmps < ipartitionsize ? ipartitionsize + ksmps : ipartitionsize)/sr
prints "Convolving with a latency of %f seconds%n", idel
; actual processing
al, ar ins
awetl, awetr pconvolve kvol*(al+ar), "Mercedes-van.wav", ipartitionsize
; Delay dry signal, to align it with the convoled sig
adryl delay (1-kmix)*al, idel
adryr delay (1-kmix)*ar, idel
outs adryl+awetl, adryr+awetr
endin
instr 2
imix = 0.5 ; Wet/dry mix. Vary as desired.
ivol = .5*imix ; Overall volume level of reverb. May need to adjust
; when wet/dry mix is changed, to avoid clipping.
ipartitionsize = 32768 ; size of each convolution partion
idel = (ksmps < ipartitionsize ? ipartitionsize + ksmps : ipartitionsize)/sr ; latency of pconvolve opcode
kcount init idel*kr
; since we are using a soundin [instead of ins] we can
; do a kind of "look ahead" by looping during one k-pass
; without output, creating zero-latency
loop:
al, ar soundin "John_Cage_1.aif", 0
awetl, awetr pconvolve ivol*(al+ar),"FactoryHall.aif", ipartitionsize
adryl delay (1-imix)*al,idel ; Delay dry signal, to align it with
adryr delay (1-imix)*ar,idel ;
kcount = kcount - 1
if kcount > 0 kgoto loop
outs awetl+adryl, awetr+adryr
endin