In professional audio work, noise is a common problem, and it is difficult to determine the root cause of the problem. Generally, there are many devices that make up the audio system. The more devices, the more complex the links, and the longer the signal transmission distance, the greater the possibility of noise in the system. Now, let's introduce the causes of audio system noise.

There are four reasons for noise, including improper grounding, electromagnetic radiation interference, circuit noise inside the equipment, and noise generated by power interference.

（1） Improper grounding. In the audio system, the whole system must be well grounded. The grounding resistance should be less than 4 ohms. Otherwise. The induced charge generated by various radiation and electromagnetic induction of the equipment in the system will not flow to the ground, thus forming a noise voltage superimposed on the audio signal.

Ground potential difference exists between wires of different equipment due to different grounding resistance, or there is a loop in the system internal grounding, causing grounding noise. When two different audio systems are connected to each other, it is also possible that the ground wires of the two systems are directly connected to produce noise.

（2） Noise generated by electromagnetic radiation interference. The stray electromagnetic wave radiation interference of the environment, such as high-frequency electromagnetic wave radiation interference of communication equipment such as mobile phones and walkie talkies, electrical pulse interference such as elevators and air conditioners, and the radiation of silicon controlled rectifier control equipment for studio lighting control, will directly mix into the transmission signal through the transmission line to form noise. The reason for our No.1 studio is that there are a large number of silicon controlled dimming equipment. As a result, there is always noise in sound reinforcement.