code: def _masked_middle_begin_end(self):
          
          self._ensure_mfcc_mask()
          begin = numpy.searchsorted(self.__mfcc_mask_map, self.__middle_begin, side="left")
          end = numpy.searchsorted(self.__mfcc_mask_map, self.__middle_end, side="right")
          return (begin, end)
docs: Return the begin and end indices w.r.t. ``self.__mfcc_mask_map``,
          corresponding to indices in the MIDDLE portion of the wave,
          that is, which fall between ``self.__middle_begin`` and
          ``self.__middle_end`` in ``self.__mfcc``.
  
          :rtype: (int, int)