Frequency spectrum with fft of a real valued array...?
Holger
postbox.holger at gmx.net
Mon Jan 22 08:05:00 EST 2007
Hello Robert!
Thank you for your tips. They were very useful.
Bye Holger
Am 11.01.2007, 19:08 Uhr, schrieb Robert Kern <robert.kern at gmail.com>:
> Holger wrote:
>
>> What does it mean to me? How do I get to the wanted frequenca
>> spectrum???
>
> It's packed in the conventional FFT format. Here is a function in numpy
> (the
> successor to Numeric, which I assume that you are using) that generates
> the
> corresponding frequencies in the same packed format:
>
> In [324]: import numpy
>
> In [325]: numpy.fft.fftfreq?
> Type: function
> Base Class: <type 'function'>
> Namespace: Interactive
> File:
> /Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/numpy-1.0.2.dev3507-py2.5-macosx-10.4-i386.egg/numpy/fft/helper.py
> Definition: numpy.fft.fftfreq(n, d=1.0)
> Docstring:
> fftfreq(n, d=1.0) -> f
>
> DFT sample frequencies
>
> The returned float array contains the frequency bins in
> cycles/unit (with zero at the start) given a window length n and a
> sample spacing d:
>
> f = [0,1,...,n/2-1,-n/2,...,-1]/(d*n) if n is even
> f = [0,1,...,(n-1)/2,-(n-1)/2,...,-1]/(d*n) if n is odd
>
>
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