“The hut is in a human environment, without the noise of cars and horses.” The ancients more than a thousand years ago were full of yearning for a quiet environment. Today, human society has entered an unprecedentedly prosperous modern era, and the colorful life is inevitably eroded by various noises far exceeding the “noisy of cars and horses”. With the advancement of science and technology, a technology called Active Noise Cancellation (ANC) has made this “luxury idea” a reality, and has gradually been applied to many fields closely related to human life, such as consumer electronics, car cockpits, and smart home appliances. Taking TWS (true wireless Bluetooth headset) as an example, the active noise reduction function has also become a “just-needed” function for product market competition. “Faced with the increasingly strong demand for active noise reduction for the next generation of TWS headphones, how upstream manufacturers can help customers introduce products and quickly bring them to the market by providing high-performance chips and algorithm solutions, is the ‘second half’ competition for TWS headphones to seize the market The key to getting ahead.” Sophie, Marketing Manager of Industrial Medical Consumer Products, ADI China, said in a recent interview.

Sophie Mao, Marketing Manager, Industrial Medical Consumer Products, ADI China

Demystifying the century-old exploration history of active noise reduction technology, decoding the new explosion of TWS headphones

The history of human beings’ struggle with noise can be traced back to primitive society. Covering your ears in fear of thunder is the earliest noise reduction method for human beings. Nowadays, many related products have been derived from traditional noise reduction methods, such as earplugs, sound insulation cotton, sound insulation panels, etc., which are passive noise reduction by surrounding the ear to form a closed space, or using sound insulation materials such as silicone earplugs to block external noise. The low-frequency noise can play a good role in suppressing it, but it can’t do anything to the low-frequency noise, nor can it fundamentally solve the noise.

Active noise reduction ANC is to listen to the background noise, use the chip and algorithm model to calculate the noise sound wave and generate the anti-phase sound wave, and use the sound wave superposition and cancellation principle to achieve the noise reduction effect. Throughout its development history, 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, that is, active noise reduction. Noise reduction based on the principle of destructive interference of sound waves. In 1978, Dr. Amar G. Bose, the founder of Bose, was on a plane from Europe to Boston and found that the noise of the aircraft engine interfered with his interest in listening to music with headphones. After getting off the plane, he began to deduce the calculation and wrote noise-cancelling headphones. The original formula.

In the 1990s, ADI fellow and American Academy of Engineering Bob Adam invented and developed the world’s first single-chip Σ-Δ audio ADC, which made Bose’s noise-cancelling headphones for ordinary consumers, QuietComfort, possible. In the 21st century, ADI fellow Khiem Nguyen invented and promoted the generation of low-latency, low-power audio codec signal chains, enabling Bose engineers to launch the miniaturized noise-cancelling headphones QC20 on the basis of the noise-cancelling headphones QuietComfort. Since then It has set off a wave of “revolution” in the headphone industry. “ADI has been working with industry leaders for the past three decades, and has been at the global forefront of the ANC field, accumulating a lot of technical experience,” Sophie pointed out, “Therefore, whether it is the early launch of the programmable low-latency audio processing engine ADAU1772 or the 2017 ADAU1772 From the ADAU1777 and ADAU1787 launched in 2019 and 2019, to our latest ADAU1860, the comprehensive performance has been in the leading position in the industry for that year.”

Release of ADAU1860/ ADAU1850 developed by ADI China

　A new generation of low-power ANC chips is released, and multi-point key performance is upgraded

According to Sophie, the current digital active noise reduction is a technology widely used in the industry. Whether it is feedforward, feedback or a combination of the two (Hybrid), they are all based on microphone noise acquisition – DSP/MCU processing, and then output. Reverse phase sound waves for noise reduction. “Whether it is ADC/DAC or DSP, ADI is recognized as a leading technology company in the industry, so we have a natural leading gene in the field of ANC technology.” Sophie pointed out, “Compared with the ARM processor of firmware, DSP has extremely high performance. Great design flexibility and optimization capabilities – you can tune the filters individually or customize the software for different needs.”

ADAU1860 is a new generation of low-power active noise reduction chip launched by ADI. It is mainly composed of three parts: the first part is the ADC, which collects the external sound source and converts it into a digital signal; the middle part is two very powerful DSPs, one is the ADC. The first one is HiFi-3z DSP, which mainly realizes the recognition of audio scenes, such as uplink noise reduction and voice wake-up. The other is Fast DSP, which is extended to 96-bit instruction set. In addition to completing a set of filter algorithms of ANC, it can achieve more functions such as noise floor suppression and EQ adjustment; the third part is high-performance. DAC, the dual power rail setting of 1.2V and 1.8V on the power supply can further optimize the power consumption according to the different usage scenarios of customers.

The arm-based MCU solution mentioned by Sophie is an integrated SoC system solution that is widely used in ANC solutions in the industry. It usually integrates Bluetooth and ANC functions on a single chip. “ADI’s active noise reduction solution uses a digital processing circuit separated from Bluetooth and ANC CODEC, and a hybrid noise reduction solution. Compared with the SoC solution, this natural isolation method reduces the noise interference caused by Bluetooth transmission and reception, and brings more benefits to customers. A good sound quality experience.” Sophie added, “The most essential function of headphones is to ensure audio quality, and a good solution needs to ensure that users can enjoy the listening experience of music, which is partly determined by analog technology.”

Separation scheme vs SOC scheme

ADI uses the combined design of ADC, DAC and DSP to ensure signal quality while showing strong signal processing capabilities, and at the same time demonstrates its profound skills in small chip package and low power consumption. In response to the two major development trends of the TWS headset market being divided into basic functional types and extended types, ADI launched a functional product ADAU1860 and a simplified version ADAU1850 at the same time. The main difference between the two products is that the latter reduces the Hifi-3Z DSP and only retains the Fast DSP. “Although the audio scene recognition of ADAU1860 has been reduced, it can also help customers to achieve a very high level of ANC and complete the demands of product upgrading.” Sophie emphasized.

An excellent TWS headset needs to be comfortable to wear and use for a long time. It is suitable for various life scenarios. Therefore, from the acoustic design to the comprehensive balance of passive noise reduction and active noise reduction, it is the main point that manufacturers need to consider when designing headphones. “ADI’s new generation of active noise cancellation chips can provide reliable digital signal processing solutions for many audio and speech applications, including speech enhancement, noise reduction, echo cancellation, level control, acoustic feedback suppression, microphone arrays and active noise/ Vibration control, these allow customers to create some unique features and selling points for the headset,” added Sophie.

　Local R&D advantages + full ecological support, ADI boosts ANC to accelerate market penetration

According to Sophie, this new product is also a product developed and designed by the ADI China team completely and independently. There are three comprehensive considerations behind it:

First of all, at the hardware level, the ADI China R&D team fully integrates the product design and market demand of local customers, whether it is a large customer, a small customer or a medium-sized customer in the local consumer category, it is as close to their hardware needs as possible;

Secondly, at the software and support level, ADI’s software development tools and some algorithms are implemented locally, so it can help customers design better products using ADI’s development tools in a very short period of time;

The last point is in the supply chain, ADI will use more local suppliers, so that customers have more options to meet different demands.

“ADI’s free audio processor programming, development and debugging software Lark Studio tool provides a variety of signal processing algorithms integrated into an intuitive graphical user interface (GUI), enabling the creation of complex audio signal flows. For acoustic customers, they can also use this software to easily complete tasks.” Sophie pointed out, “Lark Studio is also a very good online real-time mixing platform, all our customers are based on Lark Studio for pre-development, including completion Prototyping.”

Although the TWS earphone market is still hot at this stage, a large part of the growth is still TWS earphones without ANC function, because ANC still has many technical barriers in development and production. In order to help more SMEs to smoothly introduce ANC solutions, ADI not only continuously innovates and continuously launches product solutions with better performance, but also strengthens software reference guidance in addition to hardware reference designs, making it easier for customers to design and mass produce. In addition, ADI also cooperates with production calibration equipment manufacturers to directly integrate ADI’s entire calibration program into it, reducing the technical threshold for customer production calibration. “ADI will cooperate with the majority of manufacturers to help them transform customers who have ANC needs, and jointly promote the popularization of ANC functions in TWS headsets. I believe that with the blessing of ANC technology, TWS headsets will not only be an accessory that improves the quality of life in the future, It will also be one of the indispensable mobile Internet portals.” Sophie concluded.