The spectrogram function returns amplitude (the ‘z’ axis of the rotated surf plot) in units of dB/Hz, so it will not produce the amplitude results that the fft function would return.
Instead, use the pspectrum function with the 'spectrogram' option, that will return the amplitude uints (again the ‘z’ axis of the rotated surf plot) of the original signal.
Compare the two funcitons with the same signal to see the difference in the results. Both of them provide the ability to get the data directly from the outputs without having to recover them from the surf plot (although that is always an option).
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