Creating a harmonizer

ajdi123

Hello everyone!

So... I've decided to embark on my second major project in Pd... a Harmonizer. basically, I want to create a phase vocoder for live usage, that is, I want to be able to sing into Pd and have my voice come out an octave/3rd/5th/etc higher/lower.

From what I understand, I'll need to use a FFT, but I have no real idea where to start with this. I'm in the process of watching the stanford web series "The Fourier Transform and its Applications"... but I don't really have time to sit through ~30 hours of videos to get one application done.

I've looked through the forum (nothing) and the help file in Pd goes clear over my head. Is there anyone out there willing to help? I know that I'd need to find the frequency, shift the frequency by x + 2^(1/12).. then resynthesize without changing the period. Right?

GAH! help please!

Thanks,
AJ

ralf

if all you want to do is pitchshifting and you don't want to bother digging through fft theory, you could just use [pvoc~] from the fftease library. it does sinebank resynthesis and sounds really nice.

in the extra~ department of this forum there's also a granular solution for pitchshifting that was recently added. just look for [soundtouch~]

ajdi123

Ralf-

I will certainly check it out! I would, however, like to learn the fft theory behind the harmonizer so I can do it my self, if only out of principal (and because it looks far more impressive). Are there any readings you could recommend?

-AJ

ralf

this is a nice introduction to general fft methods, but it only covers the very basics (no pitchshifting though):

http://footils.org/2007/02/20/beginners-guide-fft-objects-pd/

i'm no expert on pitch shifting, but as far as i know it all boils down to squeezing or stretching your blocks of spectral data (both re and im) up and down the horizontal axis. however if you want things to be sounding good and you want to shift exact halfnotes, that's where it becomes more complicated.

unfortunately i don't know of any comprehensive fft guide that's focused on pd and that that shows practical methods rather than formulas and theory. so it's a lot of research and trial and error if you want to learn that stuff.

i've attached two basic fft pitchshifting examples that might get you started.

http://www.pdpatchrepo.info/hurleur/pitchshift.zip