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From: | Roberto Hernandez |
Subject: | Re: A question on fftshift |
Date: | Sun, 21 Jul 2002 20:16:04 -0300 |
User-agent: | Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0.0) Gecko/20020530 |
Steve M. Robbins wrote:
is that the frequency interval for the FFT output is [-fc,fc] where fc is the critical (Nyquist) frequency.For an odd number of samples. Otherwise it's [-fc, fc - 1(N*Dt)].No, the samples are equally-spaced around the unit circle, with a sample always at angle zero. So you'll only get a sample halfway around (at frequency +/- fc) if N is even.
You're right, but that's not what I was referring to. If you have an even number of samples then the FFT output bins will not be on a symmetrical frequency interval [-fc, fc], rather [-fc, fc - 1/(N*Dt)] where fc=fs/2. OTOH, if N is odd, the frequency interval will be symmetrical: [-fa, fa] where fa=(N-1)*fs/(2*N).
Thanks for the patch. Regards, Roberto ------------------------------------------------------------- Octave is freely available under the terms of the GNU GPL. Octave's home on the web: http://www.octave.org How to fund new projects: http://www.octave.org/funding.html Subscription information: http://www.octave.org/archive.html -------------------------------------------------------------
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