frequency spectrum using matlab

[thasneem1]

how to get frequency spectrum of EEG signal using matlab?abs(fft(x)) is not giving good plot

 

[permute]

What specifically is wrong?

 

[ramya1]

I have EEG data sets with each data set of 257 samples.I need to perform DFT/FFT of the data.Can any one tell me the code for this in MALAB?

 

[arplon]

If by the plot does not look "good" you mean it is split and spread out its because the FFT is not centered. Use abs(fftshift(fft(x))) instead to get a centered plot.


*Edit: the order which you use fftshift does matter, it should be used after you take the fft.

 

[milind.a.kulkarni]

In my view you need to have couple of more samples to be presents for ECG to see the good frequecy correlation....or you do one thing there is function for resample the sequece....for 257 samples you will get frequency resoltion of only 128 on either side with one zero-frequecy component.... fftshift is good to view the data....but to get more accurate frequency contribution....it better to have more samples such that.... there will be good frequency resolution....

Good Luck

 

[Iuri]

Look for "spectrum" command... works really good for me.

% s7 is my data array
% fs is the sample frequency

fs = 10000;
t = 0: 1/fs : (length(s7) - 1) / fs;

[ P, F ] = spectrum(s7, 4096, 0, hanning(4096), fs);

plot( F, P );

I hope it can help you

Iuri~