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I have a seismic accelerogram. I tried to apply the Fourier Transform to interpolate function, but dosn't work. So, i applied the Fourier[signal,FourierParameters->{-1,-1}], when i Plot (ListLinePlot)

Abs[Fourier[signal,FourierParameters->{-1,-1}]]

Signal:

https://www.dropbox.com/s/tkag1h1tkbb34p8/elcentro.dat?dl=0

I obtained a Incorrect graphics (no sense ).

Signal

Fourier Transform Obtainded By Fourier[]

Can I solve It?

thanks in advance

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  • $\begingroup$ I haven't looked at your data, but I think it must be 2d, that is, a list of lists. $\endgroup$
    – mikado
    Oct 16, 2016 at 11:02
  • $\begingroup$ Have you got time mixed in with the data? The input to Fourier should be a list of the data without the time coordinate. $\endgroup$
    – Hugh
    Oct 16, 2016 at 11:02
  • $\begingroup$ @hugh so I must pass to "Fourier[]" only time coloumn? If yes, how plot The diagram frequency/Abs[FT]? Thx $\endgroup$
    – plus91
    Oct 16, 2016 at 11:07
  • $\begingroup$ @mikado I must verify but i think it is a list with two coloumn (time and acc). I import it by signal=Import["elcentro.dat"] and Then plot it by " ListLinePlot[signal]. Thx $\endgroup$
    – plus91
    Oct 16, 2016 at 11:10
  • $\begingroup$ Just use the ordinates. I put some information on using Fourier here. $\endgroup$
    – Hugh
    Oct 16, 2016 at 11:12

1 Answer 1

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Like already pointed out in the comments: only use the ordinate values.

fData=Abs[Fourier[data[[All,2]],FourierParameters->{-1,-1}]]^2;
fData=fData[[1;;Floor[Length[fData]/2]]];

With a little bit more code, we can visualize it very well:

SR=(Length[data]/data[[All,1]][[-1]]);
Frequencies=(Range[1,Length[fData]]-1)*SR/Length[data];
ListLinePlot[Transpose[{Frequencies,fData}],PlotRange->All,Frame->True,FrameLabel->{Style["Frequency",16],Style["Powerspectrum",16]},ImageSize->1200,AspectRatio->1/8]

The Powerspectrum

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  • $\begingroup$ Julien Kluge, thx for your solution ;) $\endgroup$
    – plus91
    Oct 16, 2016 at 20:13

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