[PD] Change pitch without changing length of a audio stream ?

Claude Heiland-Allen claude at mathr.co.uk
Fri Sep 21 10:06:58 CEST 2012

On 21/09/12 08:05, Charles Goyard wrote:
> Hi list,
> In a installation I'm building, I use veejay (veejayhq.net) for video
> display, and route the audio of the video for further mixing in pd. This
> works very well.
> Under some circumstances, I change the video playback speed. Veejay has
> a feature called "trickplay" that adjusts the audio to the video length
> by changing the pitch much like a 33rpm vynil record played at 45rpm.
> What I want is keep the original pitch of the sound. So I figured out
> timestretching is what to do. I can send the speed factor of the video
> to pd. So I tried the timestretch~ external, the vocoder example (got
> this advice from list archive). They both sound terrible, even with the
> audio files from the examples (bell.aiff).
> So is it something doable in real-time or do I have to look for a
> workaround ? Any advice is welcome.

Real-time timestretch is a hard problem.  (Timestretch itself is hard).

I'd see how mixxx does it (possible wrong number of x there, but it's a 
free DJ-style software with sources available last time I checked). 
Then see if it's time stretch suits your needs and rip it out into a Pd 
external - possibly with luck mixxx just uses a library to do the dirty 
work so it might be a quick job.


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