I still think this is the wrong way to go, and that axes.specgram should pass None arguments through to mlab.specgram so the defaults in mlab.specgram are used. Otherwise, the two are in danger of becoming inconsistent.

To properly format the plot, the output from mlab.specgram should be used, not the input. Given that the plotting function only uses Fs, and Fs is easily retrievable from the output (= 2 * freq[-1]) this is easily done.

(FWIW I think eventually mlab.specgram should disappear and be replaced by https://docs.scipy.org/doc/scipy-0.17.0/reference/generated/scipy.signal.spectrogram.html since Matplotlib is really a plotting library and not a spectral analysis library)

pyplot would need to be regenerated too (or #9173 merged :-)). And I agree that the whole thing should be deprecated anyways.

I'm going to close this, because its sat for quite a while and I don't think the proposed behaviour is correct. Feel free to re-open if I am mistaken.