squared fast Fourier transform of a moving boxcar filter

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Biljana basarin
Biljana basarin 2013-3-15
I need to calculate time evolving PSD or Squared fft of a signal at certain frequency using a moving boxcar filter. I need to show the variations of signal at certain frequencies over time.

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Wayne King
Wayne King 2013-3-15
Just specify the boxcar filter as the window argument in spectrogram.
t=0:0.001:2;
x=chirp(t,0,1,150);
win = 1/200*ones(200,1);
% if you want unit norm in your filter
win1 = 1/sqrt(200)*ones(200,1);
[y,f,t,p] = spectrogram(x,win,100,length(win),1E3);
The matrix, p, contains the short-time PSD estimates for a length 200 with a 100 sample overlap in the above example. Tailor it as appropriate for your case.

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