def tempo(self,
              factor,
              use_tree=False,
              opt_flag=None,
              segment=82,
              search=14.68,
              overlap=12):
        """tempo takes 6 parameters: factor, use tree (True or False), option
        flag, segment, search and overlap).

        This effect changes the duration of the sound without modifying
        pitch.
        """
        self.command.append("tempo")

        if use_tree:
            self.command.append('-q')
        if opt_flag in ('l', 'm', 's'):
            self.command.append('-%s' % opt_flag)
        self.command.append(factor)
        self.command.append(segment)
        self.command.append(search)
        self.command.append(overlap)
        return self
tempo takes 6 parameters: factor, use tree (True or False), option
        flag, segment, search and overlap).

        This effect changes the duration of the sound without modifying
        pitch.