code: def masked_middle_map(self):
          
          begin, end = self._masked_middle_begin_end()
          return self.__mfcc_mask_map[begin:end]
docs: Return the map
          from the MFCC speech frame indices
          in the MIDDLE portion of the wave
          to the MFCC FULL frame indices.
  
          :rtype: :class:`numpy.ndarray` (1D)