From: Adam Shelly <adam.shelly@...>
Date: 2006-06-02T14:41:19+09:00
Subject: Re: Time domain to frequency domain with FFT from GSL

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The items after N/2 are the "negative frequencies"  Some mathematician can
tell you what that means, but in practical terms, they are a mirror image of
the first half (at least for audio signals).
If all you are trying to do is display (or extract information about) the
spectrum, you can throw the 2nd half of the vector away.

-Adam

On 6/1/06, Alex Polite <notmyprivateemail@gmail.com> wrote:
>
> Howdy.
>
> I need to do some Fast Fourier Transforms for an audio project I'm
> working on. Problem is I don't know shit about math ;)
>
> Reading a dozen online tutorials on FFT tells me that the FFT of a
> vector of real time domain data of size N should yield a vector of
> frequency domain data of size N/2.
>
> So I try out the different FFT functions in GSL, but the ones that
> accept a vector of real data of size N also return a vector of size N.
>
> What's the deal here?
>
> --
> Alex Polite
> http://flosspick.org - finding the right open source
>
>

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