FFT

From: Valeri Onuchin <Valeri.Onoutchine_at_cern.ch>
Date: Mon, 16 Mar 2009 08:58:09 +0100


Hi ROOTers,
I have questions concerning FFT (ROOT svn head, fftw-3.2.1, win32). I didn't find answers neither in the ROOT nor fttw3 docs. An macro (attached) is based on the the ROOT tutorial. I cant figure out the following:
1. how to scale x-axis on the pad "Magnitude of the 1st transform"

   in order to have "real frequency"
2. how to scale y-axis on the pad "Magnitude of the 1st transform"

   in order to have "real magnitude"
3. I found that "frequency reconstruction" ("Magnitude of the 1st transform" hist)

   drastically depends on the number of samples (n parameter in the macro) and    range (upX). Could you recommend a procedure for their calculation? 4. I see that magnitudes of frequencies are different (but they should be equal).

How to correctly find/reconstruct magnitudes?

I posted these questions in the list because of urgency. Please, answer to me directly or at
http://root.cern.ch/phpBB2/viewtopic.php?p=34633

Thanks.

Regards. Valeriy

Received on Mon Mar 16 2009 - 08:58:19 CET

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