Application of ANC Technology for TWS Headphones
Since Apple launched AirPods in 2016, the emerging category of split true wireless (TWS) earphones has been gradually solved by virtue of the extreme convenience brought to consumers and the pain points such as transmission, battery life, and price, detonating a new round of growth. volume market. According to the "Global Bluetooth Headset Sales and Revenue Forecast 2001-2024" research report released by Strategy Analytics, a world-renowned research institution, the sales of TWS Bluetooth headsets increased by 200% in 2019, and the market size of TWS headsets is expected to reach 100 billion by 2024. Dollar. At a recent event, domestic TWS headsets are still in the stage of extensive growth, and players at all levels will fully enter this market.
The ANC (Active Noise Cancellation) function is becoming a standard feature of TWS headphones due to its practicality, and it is expected that more than half of TWS headphones will be equipped with the ANC function by 2023. Therefore, how to add excellent noise reduction function to small and portable TWS earphones is becoming the key focus of current earphone manufacturers' product design. As a world-leading supplier of data conversion and signal processing technology widely recognized in the industry, ADI provides the industry's unique dedicated ANC SoC solutions, and has been used in the flagships of leading audio manufacturers at home and abroad such as Bose, Baohuaweijian, Wanmo, etc. It has been widely used in products.
Cracking the secret to quiet, this noise-canceling tech is going mainstream
In fact, for TWS headphones, the most basic needs of users are portability and long battery life. On top of this, users' main needs are a clear and clean listening experience. Today, when environmental noise floods our various life scenes all the time, this requirement is not easy to achieve, and the demand for noise reduction is getting higher and higher. Although passive noise reduction by enclosing the ear to form a closed space, or using sound insulation materials such as silicone earplugs to block external noise can play a good role in suppressing high-frequency noise, it cannot do anything for low-frequency noise, and it depends on low-frequency noise. on Active Noise Cancellation. The active noise reduction function is to generate anti-phase sound waves equal to the external noise through the hardware noise reduction system to neutralize the noise, so as to achieve the effect of noise reduction.
According to Sophie Mao, active noise reduction has both analog and digital noise processing circuits. Although the analog circuit has basically zero delays and the digital circuit has a delay, the analog active noise reduction circuit has many components, large PCB size, and high precision requirements, so digital noise reduction is the current mainstream. In addition, in terms of flexibility, the analog active noise reduction method is limited, mainly focusing on volume adjustment, while the digital active noise reduction can optimize the noise reduction effect by adjusting the gain, EQ coefficient, and updating the firmware. The consistency of the analog active noise reduction circuit is very poor, and it needs to be adjusted and calibrated repeatedly on the hardware; the digital active noise reduction has a good consistency, and there are corresponding adjustment tools and software to easily achieve the calibration. Finally, the BOM cost of analog active noise reduction seems to be below, but the defect rate and rework rate are high, and the overall mass production cost is actually higher than that of digital circuits. Therefore, analog active noise reduction is gradually becoming a thing of the past, and digital active noise reduction has become the mainstream of the market.
Analog noise reduction processing circuit vs digital noise reduction processing circuit
In terms of implementation, active noise reduction can be divided into three types: FeedForward, Feedback, and a combination of the two (Hybrid). Feedforward active noise reduction headphones are generally located outside, collect noise and then send it to DSP for processing, and then output reverse-phase sound waves for noise reduction. The microphone of the feedback active noise reduction headset is located inside the cavity, and the noise collected and input to the DSP is basically the same as what the ear hears, and can be directly inverted. The hybrid active noise reduction combining the two methods can achieve faster and better 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 definitely become the first choice for manufacturers." Sophie Mao emphasized. ADI's ADAU1787 SoC solution provides a 4-channel ADC input interface and 4-channel digital microphone input, which is suitable for mixed noise-canceling headphones.
△ANC (Active Noise Cancellation) chip monitors both the noise generated by the external source and the sound played by the headphone speaker through the built-in microphone
Chip software modular solution to solve the core pain point of headphone ANC
Therefore, the focus of TWS earphone noise reduction is to accurately collect noise, quickly process and output canceled anti-phase sound waves, and at the same time have the lowest possible power consumption to achieve long battery life. The three core parts of active noise reduction are ADC, DSP, and DAC. As ADI, which has always been leading in high-performance analog technology and digital signal processing technology, has naturally gained the first-mover advantage in ADC, DAC, and DSP, and can handle it delicately. The most sensitive microphone signal in the ANC system, while ensuring ultra-low power consumption, shows strong signal processing capabilities, and at the same time demonstrates its profound skills in small chip packages and low power consumption.
