[PD] delay compensation in pitch-shifting

Maximiliano Estudies maxiestudies at gmail.com
Tue Nov 24 14:59:17 CET 2020


Hi Hans,

how are you measuring the delays?

Cheers,
Maxi

El vie, 20 nov 2020 a las 15:25, info at hansroels.be (<info at hansroels.be>)
escribió:

> Hello,
>
> Hopefully people with more knowledge of audio processing can answer the
> following questions. Background: I make patches in which the microphone
> input is modified by different kinds of pitch-shifting, I would like to
> compensate the delays caused by these pitch-shifts and thus avoid
> artefacts.
>
> 1) How much delay does a pitch-shifter based on a variable delay (the
> classic rotating-tape-head style) produce? as in G09.pitchshift.pd in the
> audio.examples folder. I did a quick test with a one-sample-audio-trigger
> going immediately to the first channel of a recording patch in Pd and
> simultaneously going to a variable delay pitchshift (pp.pitchshift~ from
> AudioLab), routed into the second channel of the recorder. The delays are
> quite large and vary between 30 and 80 milliseconds, there seems to be no
> relation with the amount of pitch-shift. In the pitch-shifting patch I also
> notice that the delay varies between zero and the window size. Is there a
> way/patch to calculate and compensate for this delay? (for example, if you
> want to combine the original with the pitch-shifted signal in a patch). Or
> is this impossible because the delay is variable...
>
> 2) I'd like to know the delay in ms with FFT processing if you have a 1024
> sample window with overlap factor of 4, for example, in a pitch-shifting
> vocoder? I found this info on a MAx/MSP mailing list, is it correct?: "The
> I/ O delay is equal to the window size minus the hop size (e.g., for a
> 1024-sample FFT window with an overlap factor of 4, the hop size is equal
> to 256, and the overall delay from input to output is 768 samples)"; at
> 44100 sampling rate this is around 17ms delay (for a window of 1024
> samples, overlap 4).
>
> 3) Conclusion: any pitch-shifting technique introduces tens of
> milliseconds delay? (Pitch-shifting based on granular synthesis is not a
> solution, I think it also requires a buffer of at least 50ms.)
>
> Hans
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Maximiliano Estudies
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