Return the MFCC speech frames
        in the MIDDLE portion of the wave.

        :rtype: :class:`numpy.ndarray` (2D)

def masked_middle_mfcc(self):
        """
        Return the MFCC speech frames
        in the MIDDLE portion of the wave.

        :rtype: :class:`numpy.ndarray` (2D)
        """
        begin, end = self._masked_middle_begin_end()
        return (self.masked_mfcc)[:, begin:end]