In the audio work of radio and television, the noise problem is a common and difficult problem to judge. The more equipment constitutes the audio system, the more complex the links are, and the longer the signal transmission distance is, the greater the possibility of noise in the system is. Now, we will introduce the causes and solutions of noise in the audio system.

1、 Causes of noise

（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.

（3） Circuit noise inside the equipment

When one equipment works alone. The electrical noise generated by internal electronic components can meet the required standard, but after multiple devices are cascaded, the noise will accumulate and increase, forming serious noise in the system.

（4） Noise generated by power interference

Due to the common access of various lighting equipment, power equipment and control equipment, urban power grid has formed a serious interference source. For example, lighting control equipment, air conditioners, motors, etc. connected to the same power grid will generate spikes, surge currents, and ripple voltages of different frequencies on the power lines. Enter the power supply of the equipment through the power cord. There will always be a part of interference noise voltage that cannot be effectively filtered through the power circuit of audio equipment, which will inevitably form noise inside the equipment.