Corrected default values of xextent in specgram(). Fixes Bug matplotlib#7666.

Author: DietBru

lib/matplotlib/axes/_axes.py

@@ -7104,14 +7104,14 @@ def specgram(self, x, NFFT=None, Fs=None, Fc=None, detrend=None,
         Parameters
         ----------
         x : 1-D array or sequence
-            Array or sequence containing the data
+            Array or sequence containing the data.
 
         %(Spectral)s
 
         %(PSD)s
 
         mode : [ 'default' | 'psd' | 'magnitude' | 'angle' | 'phase' ]
-            What sort of spectrum to use.  Default is 'psd'. which takes
+            What sort of spectrum to use.  Default is 'psd', which takes
             the power spectral density.  'complex' returns the complex-valued
             frequency spectrum.  'magnitude' returns the magnitude spectrum.
             'angle' returns the phase spectrum without unwrapping.  'phase'
@@ -7139,10 +7139,11 @@ def specgram(self, x, NFFT=None, Fs=None, Fc=None, detrend=None,
             A :class:`matplotlib.colors.Colormap` instance; if *None*, use
             default determined by rc
 
-        xextent :
-            The image extent along the x-axis. xextent = (xmin,xmax)
-            The default is (0,max(bins)), where bins is the return
-            value from :func:`~matplotlib.mlab.specgram`
+        xextent : [None | (xmin, xmax)]
+            The image extent along the x-axis. The default sets *xmin* to the
+            left border of the first bin (*spectrum* column) and *xmax* to the
+            right border of the last bin. Note that for *noverlap>0* the width
+            of the bins is smaller than those of the segments.
 
         **kwargs :
             Additional kwargs are passed on to imshow which makes the
@@ -7156,14 +7157,14 @@ def specgram(self, x, NFFT=None, Fs=None, Fc=None, detrend=None,
         Returns
         -------
         spectrum : 2-D array
-            columns are the periodograms of successive segments
+            Columns are the periodograms of successive segments.
 
         freqs : 1-D array
-            The frequencies corresponding to the rows in *spectrum*
+            The frequencies corresponding to the rows in *spectrum*.
 
         t : 1-D array
-            The times corresponding to midpoints of segments (i.e the columns
-            in *spectrum*)
+            The times corresponding to midpoints of segments (i.e., the columns
+            in *spectrum*).
 
         im : instance of class :class:`~matplotlib.image.AxesImage`
             The image created by imshow containing the spectrogram
@@ -7228,7 +7229,9 @@ def specgram(self, x, NFFT=None, Fs=None, Fc=None, detrend=None,
         Z = np.flipud(Z)
 
         if xextent is None:
-            xextent = 0, np.max(t)
+            # padding is needed for first and last segment:
+            pad_xextnt = (NFFT-noverlap) / Fs / 2
+            xextent = np.min(t) - pad_xextnt, np.max(t) + pad_xextnt
         xmin, xmax = xextent
         freqs += Fc
         extent = xmin, xmax, freqs[0], freqs[-1]