Plotting the FFT of a signal with Matlab e.g. by the code:
y_fft = abs(fft(y)); f = fs*(0:length(y)-1)/length(y); plot(f,y_fft);
y is the discrete signal and 'fs' is sample rate. creates a plot where the curve can be mirrored in the middle of the x-axis e.g.
Why can the FFT always be mirrored in the middle of the x axis?