[chuck-users] pitch tracking in ChucK

[Hans Aberg]

On 12 Dec 2009, at 19:32, Kassen wrote:

>> Do these track the overtones? - When checking the spectrum of an  
>> oud, I noticed that the fundamental is missing if one passes to new  
>> note by shortening the string with the finger against the board  
>> without striking it with the other hand.
>
> Well, fft as such doesn't "track" anything.

In a past thread, when discussing using GPUs for getting extra  
computing power, I forgot to mention this FFT that achieves 144 Gflop/ 
s on the now not so new GeForce 8800GTX:
   http://en.wikipedia.org/wiki/OpenCL

Haven't looked at details, but I think it can be used as just an added  
parallel computing resource.

> All you get is energy and phase for a certain band over that frame.  
> From this we can quite easily determine the most prominent  
> frequency, but as you know that need not be the fundamental. It  
> quite likely is the fundamental for many signals but we don't *know*  
> this and without more knowledge about the piece we can't say what  
> the root of a certain chord is, even if we could manage to separate  
> the notes. Pitch trackers often get very confused by chords (and may  
> output all sorts of musically interesting "garbage" in response).
>
> What we can do -given enough frequency resolution- is try to find a  
> series of harmonics and use that to calculate what the fundamental  
> must have been. Harmonics will be integer multiples of the  
> fundamental, after all. This is what our hearing psychology does  
> when listening to something like your oud.

Actually, the cochlea produce difference tones which do not exist  
acoustically. And if the input is a harmonic series with missing  
fundamental, it will be restored by that.

So one idea might be to add such difference tones as a part of an  
analysis.

   Hans