MATLAB: Help in understanding the Power Spectral Density estimates using FFT

fftpower spectral densitySignal Processing Toolbox

I came across this article in documentation which has this particular line:
psdx(2:end-1) = 2*psdx(2:end-1);
I couldn't quite get why only the indices 2 to last but one is taken i.e, first and last indices are discarded.
It would be great if anyone could help me understand why this is being done.

Best Answer

  • hi
    the explanation is just above
    Zero frequency (DC) and the Nyquist frequency do not occur twice.
    thats why the factor 2 on the psdx amplitude does not apply to indice "1" and "end"