Noise can be reversed, provided that the real-time noise elimination is very accurate. In the actual listening process, all the sounds we often hear can be decomposed into acoustic signals with different wavelengths and amplitudes, which can be represented by waveform images. When the noise-reducing earphone collects the environmental noise through the microphone, it is transmitted to the noise-reducing circuit to analyze the noise waveform, and then the waveform with the same amplitude and opposite phase is generated in real time to cancel it. After the cancellation, the sound amplitude will be reduced, and the noise that originally sounded loud will be reduced, but if the amplitudes of the two sound waves are just equal, the noise will disappear completely. But in fact, to realize this principle, technology is a serious injury. It is also quite difficult to synchronize the inverted signal to eliminate noise. It takes some time to generate the inverted noise with the same amplitude and opposite phase to the original noise from the ambient noise set-the noise signal is transmitted to the control circuit, and the control circuit performs real-time operation to determine the noise reduction effect. Good noise reduction products will be very accurate in this link, and will not produce residual noise signals, that is, for example, when you turn on the noise reduction switch while listening to the active noise reduction headphones, you will not hear a small amount of "buzzing" noise in your ears, and the sound in your ears will be clear and clean, and there is no noise. Many manufacturers of active noise-reducing headphones on the market have not done this, and selling them at a high price may not necessarily have the effect you want. The essence of sound is wave. If the function of inversion can be realized, some frequencies can be cancelled theoretically, such as active noise reduction. If it's just the opposite direction, it's hard to say.