def off(self):
        """!
        \~english
        Close Audio output. set pin mode to output
        @return a boolean value. if True means close audio output is OK otherwise failed to close.

        \~chinese
        关闭音频输出。 将引脚模式设置为输出
        @return 布尔值。 如果为 True 关闭音频输出成功，否则关闭不成功。
        """
        isOK = True
        try:
            if self.channelR!=None:
                sub.call(["gpio","-g","mode", "{}".format(self.channelR), self.PIN_MODE_OUTPUT ])
        except:
            isOK = False
            print("Close audio right channel failed.")

        try:
            if self.channelL!=None:
                sub.call(["gpio","-g","mode", "{}".format(self.channelL), self.PIN_MODE_OUTPUT ])
        except:
            isOK = False
            print("Close audio left channel failed.")
        return isOK