ANC noise reduction solution opens up a broader blue ocean for TWS

Since Apple created the TWS (true wireless headset) market, TWS has quickly become popular in the market due to its convenience and anytime use. In just a few years, it has transformed from a blue ocean to a red ocean market. According to Zhiyan Consulting data statistics, from 2017 to 2018, the global TWS headset market size increased from US$2 billion to US$5.376 billion, and global TWS headset shipments increased from 20 million units to 65 million units. It is estimated that in 2020, the global TWS headset market size will exceed US$11 billion, and shipments will reach 150 million units. Some industry insiders even predict that in the next five years, TWS headset shipments will exceed 1 billion units, becoming the "number one player" in the future headset market.

TWS earphones are applicable in more scenarios and their products are more and more differentiated, including sports models that emphasize wearing stability and are waterproof and sweat-proof; music earphones that are continuously optimized for appearance and sound quality; and in terms of gaming scenarios, there are also product options for extremely low latency and game audio tuning. TWS can be said to be one of the product lines with the highest volume and attention in the consumer audio equipment market in recent years. In today's market, TWS earphones equipped with ANC (active noise reduction) technology are also known as the mainstream in the blue ocean. As a global leading supplier of data conversion and signal processing technology widely recognized by the industry, ADI provides a dedicated ANC audio solution with unique advantages in the industry, with low latency, low power consumption, small size and other characteristics, which can meet different design needs such as standard, mainstream and special according to customer needs.

Noise is everywhere, ANC gives your ears a quiet world

Noise is constantly interfering with our study, work and life. If we want to take a quiet rest or listen to music, we need ANC technology to help us and give our ears a quiet world. Active noise reduction has always been a problem that audio manufacturers are committed to solving. Apple launched AirPods Pro in 2019, and its biggest improvement is the addition of active noise reduction function.

There are two ways to reduce noise in headphones, active noise reduction and passive noise reduction. Active noise reduction is to neutralize the noise by generating reverse sound waves equal to the external noise through the noise reduction system, thereby achieving the effect of noise reduction. Active noise reduction headphones have noise reduction circuits to counter external noise, while passive noise reduction headphones mainly form a closed space by surrounding the ears, or use sound insulation materials such as silicone earplugs to block external noise. Since the noise of passive noise reduction headphones is not processed by the noise reduction circuit chip, it can generally only block high-frequency noise, and the noise reduction effect on low-frequency noise is not obvious. Therefore, passive noise reduction has gradually become a thing of the past, and active noise reduction has become the mainstream of the market.

The ANC chip uses a built-in microphone to monitor both the noise generated by external sources and the sound played by the headphone speakers

The concept of active noise reduction has a long history. Which existing solutions are the best?

In the early 20th century, acoustic experts began to consider starting from the noise itself to achieve the purpose of reducing noise. As early as 1933, German physicist Paul Lueg proposed the concept of active noise control, or active noise reduction, using the principle of destructive interference of sound waves to reduce noise. In 1978, Dr. Amar G. Bose, the founder of Bose, found that the noise of the aircraft engine made him lose interest in wearing headphones to enjoy music on a plane flying from Europe to Boston. This inspired him to conduct a study on noise reduction technology at BOSE. In the end, BOSE created a pair of headphones that can reproduce human voices and music with high fidelity and significantly eliminate unnecessary cabin noise.

In the 1990s, ADI fellow and US National Academy of Engineering academician Bob Adam invented and developed the world's first monolithic Sigma-Delta audio ADC, making it possible for Bose to launch the QuietComfort noise-canceling headphones for ordinary consumers. In the 21st century, ADI fellow Khiem Nguyen invented and promoted the generation of low-latency, low-power audio codec signal chains, allowing BOSE engineers to launch the miniaturized noise-canceling headphones QC20 based on the QuietComfort noise-canceling headphones, which has since set off a wave of "revolution" in the headphone industry.

In theory, active noise reduction is very simple, but in reality, there are various technical difficulties in design. For example, how to accurately sense noise and how to ensure that the noise sound waves are completely offset. For this reason, there are three different active noise reduction technologies designed for active noise reduction, which are mainly divided into feedforward, feedback, and a combination of the two. Feedforward active noise reduction headphones are generally located outside, and after collecting noise, they are sent to the DSP for processing, and then the inverted sound waves are output for noise reduction; the microphone of the feedback active noise reduction headphones is located inside the cavity, and the noise collected and sent to the DSP is basically the same as what the ear hears, and can be directly processed in reverse phase; the hybrid active noise reduction that combines the two methods can achieve faster and better noise reduction effects. ADI is one of the first companies to develop hybrid noise reduction. At present, although the cost of hybrid active noise reduction is relatively higher, as the cost of chips and microphones decreases, this method that can bring a better listening experience will surely become the first choice of manufacturers.

As can be seen from the above figure, the three core parts of active noise reduction are ADC, DSP and DAC. ADI uses its own high-performance analog technology and digital processing technology to launch a series of dedicated noise reduction solutions, such as the low-power codec ADAU1787, which can provide 4 ADC input interfaces and 4 digital microphone inputs, and these input ports are parallel inputs, which can realize the application of a single chip in hybrid noise reduction headphones. At the same time, ADAU1787 has a unique dual-core design. The FastDSP core is used for active noise reduction filter processing, and the SigmaDSP core is used for EQ post-processing to compensate for the low-frequency part of the music lost after noise reduction processing. In addition, the ADAU1787 2.3*2.8 mm BGA package consumes only about 6-7mW when powered by 1.8V, because this solution is very suitable for TWS headphones with more stringent requirements on power consumption and chip volume.

It is reported that ADI's active noise reduction solution adopts a solution that separates Bluetooth and ANC CODEC. This "natural" isolation method reduces the noise interference caused by Bluetooth transmission and reception. Its advantage is that power consumption can also be calculated separately: when active noise reduction is turned on without listening to music or when listening to music without active noise reduction, all ANC-related components will be dormant. However, if it is not a separate solution, the battery life of the Bluetooth chip will usually decrease if it is equipped with noise reduction itself, because it cannot sleep part of it, which is also one of the advantages of ADI's noise reduction solution. In addition, considering the degree of integration, ADI can currently make the ANC solution into a module, and integrate its Sigma Studio configurable software into the system solution through the chip + software method. The advantage of this tool is that it allows code to be generated by dragging and dropping modules. Therefore, non-programmers can also easily get started with the software, which is very suitable for customers who do not understand programming but are proficient in acoustics.

summary

After years of vigorous development, the headphone market with ANC function is in a stage of extensive growth, and players at all levels will fully enter this market. At the recent Asian Bluetooth Headset Show (Winter), Zhao Yimiao, general manager of ADI China Product Division, said that digital audio chips are an important product direction of ADI China. After cooperating with mainstream manufacturers and gaining high recognition, they will further strengthen cooperation with upstream and downstream of the industry ecosystem to optimize ANC solutions to make them more performant, easier to use, and benefit more market participants, jointly promote the healthy development of the ANC technology market, and let more people enjoy the charm and fun of technological progress.