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### jit.fft

Aug 09 2006 | 12:04 am

Ok I know for audio when you do an fft on a signal you specify the size of the fft(frequency resolution). Then you get a vector of complex numbers that represent the magnitude and phase of frequencies that correspond to fs/2*n*(freqres) where n is the index of the vector…. (in the looses sense here). So my question is what exactly is the format that jit.fft spits out. Since it operates on two plane matrices I’m guessing that this will determine what data is spit out. Can someone help me understand this object?

Aug 09 2006 | 12:34 am

On Aug 8, 2006, at 5:04 PM, Tyler Nitsch wrote:

>
> Ok I know for audio when you do an fft on a signal you specify the
> size of the fft(frequency resolution). Then you get a vector of
> complex numbers that represent the magnitude and phase of frequencies
> that correspond to fs/2*n*(freqres) where n is the index of the
> vector…. (in the looses sense here). So my question is what exactly
> is the format that jit.fft spits out. Since it operates on two plane
> matrices I’m guessing that this will determine what data is spit out.
> Can someone help me understand this object?

I’d suggest you check out the jit.fft-threshold.pat example and other
jit.fft examples and let us know if you have additional questions. Keep
in mind that in an fft, you have both positive and negative frequencies
(about the center vertically and horizontally in the 2D case), and that
in a 2D fft the harmonics have frequencies about each axis as
determined by the cell position. real and imaginary coordinates are in
the matrix planes 0 and 1 respectively. More info on 2D ffts can be
found online.

-Joshua

Aug 09 2006 | 6:27 am

Thanks for the tips. Ok for future browsers and searchers of this topic after doing a little bit of digging and weeding I finally found an article that explains the relation between locations and values of the 2d fft and the actuall spatial image.

http://homepages.inf.ed.ac.uk/rbf/HIPR2/fourier.htm

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