Re: Finding audio frequency
Re: Finding audio frequency
- Subject: Re: Finding audio frequency
- From: Paul Bruneau <email@hidden>
- Date: Tue, 26 Jan 2010 11:30:03 -0500
On Jan 26, 2010, at 10:29 AM, Ian Kemmish wrote:
My analysis/resynthesis module needs accurate estimates of
frequency. What I do is take several FFTs at different times. Find
some peaks in each FFT. Sort the peaks roughly into bins (one for
each harmonic, basically). Throw out any obvious outliers in each
bin. Calculate the media frequency for each bin. Then look at the
median frequencies you have left, and see if they form an obvious
harmonic series. If they do, the harmonic is the least common
difference between them.
In the real world, remember that you have to deal with situations
where the fundamental is not necessarily the loudest harmonic. And
for plucked string instruments, the frequency of oscillation is
falling ever so slightly for as long as the string sounds (the time-
averaged tension of the string is reducing as the amplitude
decreases). And for stiff strings the partials aren't *quite*
harmonically related (which is also why looking for zero crossings
in the time domain isn't the best idea - the shape of the waveform
changes gradually).
Hope this gives you some ideas to try.
I want to thank everybody for all the pointers. Thanks for the links
to the FFT info--I had heard of this before and I'm glad to know it's
something I should learn more about.
It's not a guitar tuner (those are readily available :), it's more of
a guitar "reader".
To Ian, I hope I don't have to get as complicated as above for this.
In my mind (maybe in the real world), the string is vibrating at a
fundamental rate (that I admit will change over time). This is all I
care about. So with some internet-provided audio as an example, I
expect to see something like this (I hope this list will accept a
small picture):
I know that there are harmonics in this, but all I want to know is how
many times per second (on average over my sample as was mentioned by
Ian) the string oscillates.
Thanks again, I'm reading all your links :)
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