Issue seen in matplotlib 1.5.3, Linux, installed with pip.

Retesting software that was originally written in matplotlib 1.4 times, I am noticing a huge discrepancy in psd plots.

It looks like recent matplotlib mlab.psd fails to properly normalize the psd wrt the window size NFFT (at least when scale_by_freq is set to False).

As a result psd plots (in dB) are shifted up and down when the NFFT parameter is changed.

It is unclear to me if this is an intended result. In any case, it does not seem to be documented.