I have a beginners question about FFT analysis. I have two signals and I want to see the amplitudespectrum of them. I used the following code which was derived from the program desribed under mathworks.
Fs = 200;
T = 1/Fs;
L = length (marker(1,2).C7);
t = (0:L-1)*T;
NFFT = 2^nextpow2(L);
Y = fft(y,NFFT)/L;
f = Fs/2*linspace(0,1,NFFT/2+1);
marker(1,2).C7 is the signal I want to analyse.
The following problem occured: If I run this program on two different signals I get the same amplitudespectrum for both although the signals are different. This cannnot be true as I wanted to compare the amplitudespectrum of the signal before and after it was filtered. Although they were filtered and they looked different when I ploted them the amplitudespectrum plotted with the above code showed no differences at all. Can anybody point out where I made a mistake?
Thank you for your help,