[chuck-users] pitch tracking in ChucK

Kassen signal.automatique at gmail.com
Sat Dec 12 13:32:01 EST 2009


> 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. 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.
It's also why a HPF set loose on a full mix by a DJ in a club will sound
less dramatic that a LPF; it's far easier for us to imagine the missing
elements in the first case than the second.

I think that might've answered your question but I'm well aware that it only
raises more. There are lots and lots of questions here. Nobody knows all the
answers, in fact we are sure we will never get perfectly accurate
instantaneous pitch-tracking. I'm not even sure that would be as useful as
making good guesses based on how sound is experienced by our hearing
psychology; as noted the perceived frequency, the most important thing, may
not actually be there in the signal at all. In a way it's a bit of a tragic
task, but of course lots of fun are still to be had.

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