[linux-audio-user] changing speed without changing pitch

Stuart Allie allies at hydstra.com
Tue Oct 22 18:09:00 EDT 2002


I *finally* got around to trying the csound method of changing the speed of
an audio file without changing the pitch, but it didn't work for me :(

I used the following "orc" file:

> sr        =         44100
> kr        =         4410
> ksmps     =         10
> nchnls    =         1
>           instr     1
> 	  kfreqscale	=	1
> 	  ispecwp   =         0
> 	  ktime     line      1, p3, 0
> 	  apvl       pvoc      ktime, kfreqscale, "file.pvc", ispecwp
> out apvl	  
> endin

and then the "sco" file:
> i1 0 12 
> e

with a 6 second sample, so this should double the audio to 12 seconds. I did
the PV analysis like this:

> csound -U pvanal -n 1024 -w 4 file.wav file.pvc

and then ran csound via:

> csound -W -R -d file.orc file.sco -o slow.wav

and then I waited for a little while :)

When csound was done, the ourput file was, well, interesting...
Basically the input file was 6 seconds of single-note guitar playing, and
the output was a weird (though not unpleasant :) whooshing-sweeping-phasing
sound for 2 seconds, then a faint LFO-type sound to the end of the file. No
sign of the original clip, slowed or otherwise.

Can anybody out there tell me what I (or csound :) did wrong?

Thanks in advance,


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