Item Type: Audio Isolator Module_x000D_ Model: XH-M372_x000D_ Circuit Board Specification: Approx. 45 x 30mm / 1.8 x 1.2in_x000D_ What is common land?_x000D_ This product is an audio common ground isolator, which is effective for the noise caused by the common ground for the audio source and the receiving device._x000D_ To put it simply, a common ground is that the ground points of two electrical appliances are not at the same point. Because of the difference in ground resistance, noise is transmitted through the ground wire into the power equipment, forming interference. Because the two devices have different grounding points, common ground noise may occur. In the car audio system, there is an audio interference, which is almost the same as the whistling sound. The frequency of this noise will change with the speed of the engine._x000D_ Therefore, this product can only eliminate the noise and current sound caused by the total common-electricity products, and cannot eliminate the noise caused by other reasons. Therefore, you must confirm the source of the noise yourself._x000D_ Determine Whether the Noise is Caused By Common Ground: _x000D_ 1. Use headphones to connect with AUX (3.5mm interface) of car MP3 and car navigation. If there is no noise from the earphone at this time, it can be confirmed that the noise of the car equipment is caused by common ground._x000D_ 2. Use an audio cable to connect a battery-powered mobile phone or MP3 (note that the mobile phone and MP3 should not be connected to any power supply in the car, such as a telephone) and connect it to the AUX on the center console of the car, and play the music of the mobile phone so that there will be no noise. , you can confirm that the previous noise was caused by a total of land._x000D_ 3, Computer, Amplifier, Stereo, CD: Use passive headphones to plug in the computer to listen to whether there is noise, use the phone plug in the amplifier, audio audition, if you try to hear both without noise, the basic decision is caused by a total of._x000D_ 4, after the start of the car, the installed amplifier has a current sound, some models will appear more throttle, the greater the current sound, this product can solve this problem._x000D_ 5, there is a current sound between the amplifier and the speaker or sound, you can install this product between the amplifier and the speaker._x000D_ 6, laptops connected to the projector at the same time the power amplifier to produce noise, you can use the laptop adapter power supply or battery, then remove the power amplifier noise disappeared, or unplug the projector the same noise disappears, then you can in the computer headphone jack and power amplifier Add a common ground isolator to eliminate noise.