🚀 go-pugleaf

mikael@terapin.com (Mikael Andersson) writes:

>Was ther any results on the Pitch-shifting discussion in this conference?
>Are there any shortcuts or do i have to use FFT to change it? (And still
>keep the quality?)

You'll have problems keeping the quality with any method, since pitch-shift
is an awkward, very non-linear operation which can only really be
approximated to. There are three methods that I know of, the first of which
is the most common:

 - circular buffer, with different read-in and read-out rates. Try a buffer
   of 10 to 50ms in length.
   Main problems: discontinuities when the input and output pointers cross.

 - FFT, scale frequency, IFFT.
   Main problems: discontinuities at block boundaries, computational load.

 - Signal Modelling approach. Model the signal (eg linear prediction) and
   adjust the model parameters so that when the signal is reconstructed, it
   is at the changed pitch.
   Main problems: model choice, block boundaries, computational load.

If you want to try this, I imagine you will get best results with the first
method, though the second might be worth a go. I have no personal experience
with the third, but I believe it has been used successfully on less than 
telephone-quality speech. I doubt it would be practical for music.

> 
>Mikael

Christopher Hicks
--
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 Christopher Hicks    |    If it doesn't fit...
 cmh@uk.ac.cam.eng    |                        ...you need a bigger hammer.
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