It is widely used in systems such as automatic control, broadcasting system, audio broadcasting, power facilities and so on. In audio equipment, the correct shutdown procedure is to first turn off the power amplifier, and then turn off the audio processor, mixer and other front-end equipment in turn. The sequence is reversed when turning on. Turn off the power amplifier first in order to prevent the noise impact generated by the front-end equipment from damaging the speakers and the power amplifier.