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TWS with ANC

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Author : Eric
Update time : 2020-12-12 16:32:22
Active noise reduction technology is a technology applied to the noise reduction performance of headphones. Its working principle is to collect environmental noise through the pickup microphone above the headphones, convert the noise into a digital signal and use the built-in processor to calculate the opposite of the noise The wave, so as to achieve the effect of canceling the noise. According to its control structure classification, we usually divide it into three types: feedforward, feedback and double-feed.

Feedforward active noise reduction uses a feedforward active noise control system (open-loop noise control system). This system generally requires sound information of the primary sound field to be controlled, usually called a reference signal. The reference signal is sent to the feedforward controller. After the controller is processed, a corresponding control signal is generated, which drives the speaker to output the sound signal to generate a secondary sound field, which is then superimposed with the original sound wave signal actually transmitted through the physical channel. The error microphone detects the error signal formed by the superposition of the primary sound field and the secondary sound field, and sends it to the controller. The controller adjusts the intensity of the secondary sound source signal according to a specific algorithm.

  The advantage of this approach is that the system is an open loop, so the circuit can be debugged independently without causing any closed loop oscillation and howling. In addition, the microphone of the radio microphone is at the front end of the earphone, which can "hear" the noise much earlier than the human ear, and the system processes it in a more timely manner. The disadvantage is that it is only responsible for reporting to the noise reduction circuit and then monitoring other sounds. After the noise, the residual “leakage” noise inside the earphone.

Feedback-type active noise reduction uses a feedback-type active noise control system (closed-loop noise control system). The feedback-type system has one less reference microphone than the feed-forward system, so its system configuration is simplified. The feedback structure of the active noise control system does not need to obtain sound information in advance, but adjusts the error signal through the controller to reduce noise. Because it is a feedback system, when the gain of the amplifier is increased to a certain level, the system will become very unstable and produce high-frequency whistling or low-frequency oscillation. In order to maintain the stability of the control system, it is generally required that the position of the controller and the error microphone are very close. , And this has also led to a greatly reduced range of feedback applications.

The advantage of this processing method is that when the system monitors noise, it will detect and process the noise multiple times, and the noise processing effect is better. The disadvantage is that the position of the controller and the error microphone is very close to the response time and the reaction time is short. The closed-loop noise control system is prone to high frequency howling or low frequency oscillation.

Double-fed active noise reduction, combined with feedforward and feedback structures, is also the best design solution for noise reduction on the market. The signal emitted by the second-level sound source will be jointly determined by the reference microphone and the error microphone. The feedforward system can attenuate the noise related to the primary noise detected by the reference microphone, and the feedback system supplements the noise reduction to deal with the residual "drop-in" noise inside the earphone.

  The advantage of this processing method is that the advantages of the feedforward system and the feedback system are combined, and the noise reduction effect is stronger than any single structure noise reduction system.
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