In using spectrogram, what is the difference between specifying option 'power' and 'psd'?

I ran two tests, with identical input data, first with:

    [s,f,t] = spectrogram(y1, hann(windowsz), noverlap, nfft, fs,'yaxis','power','reassigned');

then with:

    [PSDs,f,t] = spectrogram(y1, hann(windowsz), noverlap, nfft, fs,'yaxis','psd','reassigned');

I then checked to see if the results where the same:

     if s == PSDs
        a = 'SAME'
     end

and the result was 'SAME'

So, what do options 'psd' and 'power' do?

Answer 1

[Star Strider]

The best I can do is to quote the documentation:

• Omitting spectrumtype, or specifying 'psd', returns the power spectral density.
• Specifying 'power' scales each estimate of the PSD by the equivalent noise bandwidth of the window. The result is an estimate of the power at each frequency. If the 'reassigned' option is on, the function integrates the PSD over the width of each frequency bin before reassigning.

[Jonathan]

Ok, I removed the 'reassigned' option from both spectrogram statements and I still get identical results. Any further ideas? Thanks.

Answer 2

[Greg Dionne]

The first output is always the (unmodified) STFT.

The 'power' and 'psd' and 'reassign' flags only affect the later outputs (most notably Pxx).