Clear audio from memory.

        :param audio_file: the object to clear
        :type  audio_file: :class:`~aeneas.audiofile.AudioFile`

def _clear_audio_file(self, audio_file):
        """
        Clear audio from memory.

        :param audio_file: the object to clear
        :type  audio_file: :class:`~aeneas.audiofile.AudioFile`
        """
        self._step_begin(u"clear audio file")
        audio_file.clear_data()
        audio_file = None
        self._step_end()