Hi,

 

Which window does pvstanal use? Can you use any window with timestretching/phase vocoders?

 

I am reading that the type of window is important, but am not sure if there are limitations to the type of window used:

 

“The exact shape of the window turns out to be important because the windowing operation smears the signal's spectrum so that each bin of the Fourier transform (i.e., each component in the Fourier series) includes some energy from other bins nearby”

 

Matlab’s example uses Hann(ing), but can you use a Super-Gaussian Window?

 

SG Window: SG(x;A,N) = e^((-|x/A|)^N)

 

Trying to understand the math behind it and as I’m experimenting, there are a lot of terms to experiment with, just within the window portion even. In the SG Window, for example, N is the power, A is the half-width.

 

Links/References:

• The Phase Vocoder: A Tutorial Author(s): Mark Dolson Source: Computer Music Journal, Vol. 10, No. 4 (Winter, 1986), pp. 14-27 Published by: The MIT Press Stable URL: http://www.jstor.org/stable/3680093

• https://github.com/csound/csound/blob/develop/Opcodes/pvsbasic.c

• https://www.mathworks.com/help/audio/examples/pitch-shifting-and-time-dilation-using-a-phase-vocoder-in-matlab.html

• Applications of Discrete and Continuous Fourier Analysis, H. Joseph Weaver, 1983, John Wiley & Sons Inc.

 

 

Have a good one,

Lewis

 

lewissall@Hotmail.com

 

Sent from Outlook

 

OK, sounds good. Sorry for the delay, busy at work.

 

The theory book I have says something similar, that the use/data really determines the best windowing (Weaver, 1983).

 

“Because of all these factors we can now begin to appreciate why there is no specific theory of windowing. We can only look for trends.”

 

He does highlight SG windows, that’s why I was considering it:

 

“Thus we can see why SG functions make ideal artificial windows.”

 

Hann doesn’t seem too tricky, judging by the link in Matlab, at least for experimentation.

 

w(n)=0.5(1−cos(2πnN)),0≤n≤N.

https://www.mathworks.com/help/signal/ref/hann.html

 

 

Vielen Dank!

Lewis

 

Sent from Outlook

 

 

Sep 1 2020, Lewis Sall has written:

> Hi,
>
> Which window does pvstanal use?
iwindowtype has three choices: Hamming window, von Hann window and
Kaiser window. Those are the choices.
> Can you use any window with timestretching/phase vocoders?
If you are wondering what the best window is for which purpose, I have
come to understand that this is a somewhat difficult question. In
practise you'd probably go with trial and error.
...

Best wishes,

Jeanette

--
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