I want a MATLAB implementation for Pitch Scaling (with out changing
the length) of audio signals using a Phase Vocoder algorithm. I have
already found an implementation of a Phase Vocoder for Time Scaling
(with out affecting the Pitch) of an audio signal at the following
website:

http://www.ee.columbia.edu/~dpwe/resources/matlab/pvoc-matlab.html

You can get the pitch change by applying the time change algorithm
then resampling to change the time back to what it was.

E.g 1 you want to double the pitch ..

Use Phase Vocoder to double the time for the sample (pitch unchanged,
time doubled)
Re-sample to halve the time for the sample (Pitch doubled, time
unchanged)

E.g 2 you want to halve the pitch ..

Re-sample to double the time for the sample (Pitch halved, time
doubled)
Use Phase Vocoder to halve the time for the sample (pitch halved, time
unchanged)

This should work for any change needed.

Lastly the reason e.g. 2 is done 'backwards' compared to e.g.1 is to
minimise any aliasing artifacts.

Hi, 
Thank you for you comment. 

I have tried to follow your procedure, but when I write the modified
signal into a wave file and compare the lengths of the two signals, I
notice that there is a small difference in length between them. Is
that Normal?

In an ideal world there wouldn't be any difference in length. If the
resulting .wav file sounds right I'd ignore any small changes in
length.

If it's the file length that changes it could be different header
information, there are some chunks that can be added or removed from
.wav headers without changing the sample at all.

If the sample length is changing itcould be that the phase vocoder, or
the re-sampling, is not doing exactly whatever fraction you're asking
for.

If this is the case and your sample starts or ends with silence you
could add or trim this to match the overall sample lengths.

Hope this helps.