In order to have a better listening experience, chip people are very hard

With the rapid rise of TWS Bluetooth headsets at an exponential growth rate in the past few years, active noise reduction (ANC) technology has begun to be concerned, and the scope of application has become increasingly widespread, from single-point noise reduction such as headphones to expanding to the field of noise reduction in spaces such as automobiles and homes. For example, Tesla recently loaded the function of actively reducing road noise in its new Model S and Model X. However, active noise reduction technology, especially three-dimensional space noise reduction, still has many challenges in practical applications, such as overcoming interference such as road noise and wind noise, improving the consumer experience, and enhancing market acceptance, which will be an important development direction in the future.

Single point plus space The field of application is gradually expanding

With the improvement of the quality of life, people's demand for external quiet environments is getting higher and higher. In a World Hearing Report published by the International Health Organization, hearing impairment is currently affecting 1.5 billion people worldwide, of whom 430 million have mild/moderate/severe hearing impairment. Over the next 30 years, this number is likely to increase by more than 1.5 times.

This is one of the important reasons why TWS Bluetooth headphones with active noise cancellation are favored. Audio equipment with active noise reduction technology can help people avoid external interference, improve hearing enjoyment, and reduce the damage of noise to hearing. According to IDC data, shipments of TWS wireless headphones will reach 350 million pairs in 2021, an increase of about 50% year-on-year, and the active noise cancellation function will become the mainstream specification in 2021. The market size of TWS wireless headphones is expected to reach $40.13 billion in 2024.

Active noise cancellation technology is not limited to headphones, and has begun to expand into new areas such as automobiles and homes. Tesla is in its new Model S and Model X, loaded with features that actively reduce road noise. Kelly Ann Picard, vice president and general manager of Molex's Automotive Solutions business unit, said: "With the rapid transition to electrified vehicles, reducing road noise will become critical. "Covering public transportation such as trains and airplanes, as well as off-highway applications such as heavy machinery, there is also an interest in noise reduction technology. As far as the market of automobile noise reduction is concerned, the noise sources during the driving process of automobiles can be mainly divided into several main categories such as engine noise, tire noise, road noise, wind noise, and air conditioning noise. Heavy road noise, wind noise and car HVAC noise, as well as low-frequency sounds, will interfere with driving and increase the burden on the driver. The use of active noise reduction technology avoids the installation of expensive and bulky sound-absorbing materials, and there is a huge market space.

In addition, active noise reduction technology is also applied indoors. With the continuous improvement of residential requirements, people began to use active noise reduction to control indoor noise and improve the sound environment for the noise sources of windows and household appliances. Liu Yifan, CEO of Ansheng Technology, said that the market plate in the field of home appliances is large enough, the user base is high, and the industry threshold is relatively low, which is a direction worth exploring by allowing consumers to buy new noise reduction experiences while purchasing home appliances. In the field of home appliances, more than 90% of the noise comes from the noise of wind and mechanical vibration, and targeted noise reduction product development can be carried out.

However, so far, the application of space noise reduction on the market is still relatively limited, and the main landing is more mature only in the car, but also mainly focused on the level of the car engine, and the actual application needs further exploration.

Background noise or wind noise Reality interference is still frequent

According to the data of the Institute of Acoustics of the Chinese Academy of Sciences, the principle of active noise reduction is to achieve phase cancellation by emitting sound waves with the same frequency and amplitude opposite to the noise phase. That is to say, compared with the traditional way of noise reduction by blocking sound absorption, active noise reduction can use the microphone to listen to noise waves, and then send out reverse sound waves after processing, so that the two interfere with each other during propagation, and then neutralize the noise.

This technical principle was proposed by german physicist Paul Lueg in 1933. In 1989, products with related functions were mass-produced by the professional audio brand BOSE for the first time, and the first users were pilots, airport ground crews and other personnel who were exposed to noise for a long time. In 2000, active noise reduction gradually entered the civilian market.

As things stand, although the scale of the relevant application market is getting larger and larger, the challenges faced by active noise reduction technology are also increasing due to the increasing demands of consumers. According to He Yuan, Senior Marketing Application Manager, ADI China Product Division, there are many interference items that affect the implementation of active noise reduction, including noise floor, wind noise, impact blast sound, negative pressure feeling, as well as personal use habits and product mass production efficiency.

Noise floor can be understood as the combined noise of the entire system. Noise floor is derived from the noise floor of the acoustic device, such as the electrical noise of the chip itself, the interference of Bluetooth emission, the coupling of wired and wireless devices, and sometimes the noise effect is highlighted and amplified during noise reduction debugging. These situations, if not handled well, can cause noise floor problems. When the consumer turns on the active noise reduction function in a relatively quiet scene, it is possible that the noise generated by the device is larger than the ambient noise, and the noise reduction becomes noise reinforcement.

Wind noise is also a common and difficult problem to solve. When the user turns on the active noise reduction function outdoors, the system will carry out certain processing due to the wind blowing in. The noise generated by these processes may be amplified and become more harsh. Outdoors, wind noise is a very common scene, and poor solution will greatly affect the user experience.

Active noise reduction technology is sometimes not ideal in practical applications of spatial noise reduction. Some reports reflect that the Model S turns on the active noise reduction function in rough road driving, and the ambient noise in the carriage will be reduced, but the effect is not very obvious.

Kurt Dekoski, Molex Business Development Engineer, points out that there are many challenges based on vehicle design, each vehicle has different acoustic performance, so the noise reduction system must be sufficiently adaptable and calibrated for the acoustic changes of individual vehicles.

Sensing and codec Chips play an important role

From the observation of the active noise reduction industry chain, the lowest layer is the sensor responsible for signal input and output, which monitors the environmental noise; the second layer is the signal processing chip, which analyzes the noise curve and codes the audio; and then there are enterprises with semantic understanding and intelligent interaction; and at the top is the intelligent device, data application and other related enterprises. In this chain, integrated circuit technology plays an important role.

Kurt Dekoski said: "Chip technology plays a pivotal role in driving the continued development of ANC technology. "For example, road noise reduction (RNC) sensors based on accelerometer designs can be installed on the chassis of automobiles for monitoring environmental noise to obtain more accurate and effective data to help eliminate harmful road noise, wind noise, and car HVAC noise and low-frequency sound." Technological advances to reduce the latency of electronic devices have always been key to this. Considering that it takes 0.009 seconds for the tire sound to reach the driver's ear, it is crucial to be able to transmit data from sensors near the wheels to the processing module, calculate the elimination signal and broadcast it inside the cabin. ”

When talking about how to solve the noise floor problem, He Yuan said: "We need to solve the noise floor problem from the lowest and most fundamental place, and in terms of analog technology, we must use excellent digital-analog-analog (ADC-DAC) devices to reduce noise. In terms of digital technology, a flexible instruction set is used to adjust and optimize the audio path to reduce noise from the digital end. "A high-quality ANC device even has to start at the system level, and it is necessary to consider avoiding mutual interference between devices when routing the board.

Wind noise problems can also be solved by hard decoding, such as installing a hardware-level detection module, when the microphone is perceived to be affected by external wind, immediately begin dynamic detection and adjustment to avoid the occurrence of noise. This implementation is hardware-level, and real-time and low power consumption can be guaranteed.

In short, a better listening experience has begun to receive more and more attention from people, and the entire market prospect is worth looking forward to. However, the entire industry, especially spatial noise reduction, is still in its infancy, and a series of interference problems that appear in practical applications need to be solved bit by bit by practitioners.