code: def set_volume(self, pct, channel=None):
          
  
          if channel is None:
              channel = self._get_channel()
  
          cmd_line = '/usr/bin/amixer -q set {0} {1:d}%'.format(channel, pct)
          Popen(shlex.split(cmd_line)).wait()
docs: Sets the sound volume to the given percentage [0-100] by calling
          ``amixer -q set <channel> <pct>%``.
          If the channel is not specified, it tries to determine the default one
          by running ``amixer scontrols``. If that fails as well, it uses the
          ``Playback`` channel, as that is the only channel on the EV3.