The default Hamming window length when using function 'etfe'
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In the algorithm section of 'etfe' function description it is written: You obtain the smoothed versions (_*_M less than the length of z_*_) by applying a Hamming window to the output fast Fourier transform (FFT) times the conjugate of the input FFT, and to the absolute square of the input FFT, respectively, and subsequently forming the ratio of the results.
I tried this with my 1000-point data set and plotted the frequency response using default window length setting and 1000 (my data length). The result is NOT the same. With 1000 window length the spectrum is still smoothed. I could not reproduce the default setting plot until I raised the window length to around 1340.
Could some one please explain to me why it is like this??
The code to explain what I'm talking about could be: estimate1 = etfe(testData, [], 128); bode(estimate1); estimate2 = etfe(testData, 1000, 128); bode(estimate2); Where testData is a 1000-point data set with single i/o signal.
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Wayne King
on 23 Aug 2012
Can you please provide a simple example with MATLAB code to demonstrate what you are talking about.
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