DOC: note decibel (dB) scale for specgam

ivanov · ivanov · commit 5b52fc30fa49 · 2012-11-12T13:02:50.000-08:00
diff --git a/lib/matplotlib/axes.py b/lib/matplotlib/axes.py
@@ -8610,6 +8610,7 @@ def specgram(self, x, NFFT=256, Fs=2, Fc=0, detrend=mlab.detrend_none,
           - *bins* are the time points the spectrogram is calculated over
           - *freqs* is an array of frequencies
           - *Pxx* is an array of shape `(len(times), len(freqs))` of power
+            measured in decibels (dB)
           - *im* is a :class:`~matplotlib.image.AxesImage` instance
 
         Note: If *x* is real (i.e. non-complex), only the positive
@@ -8626,6 +8627,7 @@ def specgram(self, x, NFFT=256, Fs=2, Fc=0, detrend=mlab.detrend_none,
         Pxx, freqs, bins = mlab.specgram(x, NFFT, Fs, detrend,
              window, noverlap, pad_to, sides, scale_by_freq)
 
+        # convert to dB
         Z = 10. * np.log10(Pxx)
         Z = np.flipud(Z)
 
