“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. Today, many related products have been derived from traditional noise reduction methods, such as earplugs, sound insulation cotton, sound insulation panels, etc., which are all based on sound insulation materials to block absorption and cannot fundamentally solve the noise. With the development of Electronic technology, semiconductor manufacturers such as ADI, a leading company in the field of analog signal, mixed signal and digital signal processing design, have launched their own active noise reduction technology solutions, which has gradually gained popularity in recent years.
Application of Active Noise Cancellation Technology in Noise Cancelling Headphones
Active Noise Cancellation ANC (Active Noise CancellaTIon) 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. Therefore, how to clearly distinguish different noises before they reach the ears, and then release the corresponding sound waves to cancel them, is the key to this technology.
How Built-in Noise Cancelling Headphones Work
From the perspective of the implementation of noise cancellation, active noise reduction technology can be divided into two types: the first is to use analog circuits to achieve active noise reduction, and the second is to use digital circuits to achieve active noise reduction. There are pros and cons to each noise method. The analog active noise reduction circuit requires a large number of components such as op amps, resistors and capacitors, so the PCB occupies a relatively large space, while the digital active noise reduction circuit uses a digital IC, so it occupies a small space. However, the analog active noise reduction basically has no delay, and the digital circuit will have a certain delay on the DSP. Let’s take a look at the adjustability of the noise reduction effect. The adjustment of analog ANC is very limited, and the noise reduction effect can only be changed by adjusting the gain/volume; while the digital ANC is more flexible, not only can adjust the gain, but also adjust the EQ, Noise reduction algorithms, etc. Even the headphones that have already left the factory can optimize the noise reduction effect by updating the firmware in the future. Therefore, digital active noise cancellation helps wireless audio engineers meet the full range of consumer needs, including superior sound quality, noise cancellation and suppression, and strong battery life, while at the same time because of its better noise reduction and lower Cost is gradually occupying the mainstream of the market.
Analog Active Noise Cancellation Technology vs Digital Active Noise Cancellation Technology
Based on digital active noise reduction technology, ADI has launched a series of dedicated ANC SoC chips, such as ADAU1777 ANC Audio SoC is a codec with four inputs and two outputs, built-in digital processor, can perform filtering, leveling Control, signal level monitoring and mixing. The path from the analog input to the DSP core to the analog output is optimized for low latency, ideal for noise-cancelling headphones. There are already many well-known active noise-cancelling headphones in the consumer market that use ADI’s DSP technology. For example, Bose, the inventor of noise-cancelling headphones, designed the Bose QC series of noise-cancelling headphones based on ADAU 1777, which has become a benchmark in the industry.
ADAU1777 ANC Audio SoC
The ADI ADAU1787, an upgraded version of the active noise reduction solution, integrates two digital signal processors (DSPs) – programmable FastDSP audio processors with a sampling rate of up to 768kHz, supporting biquad filters, limiters, Volume control, mixing; SigmaStudio can be used for visual programming, 28-bit SigmaDSP audio processing core with performance up to 50MIPS. … .. The path from the analog input to the DSP core to the analog output is optimized for low latency, and by incorporating a small number of passive components, the ADAU1787 provides a high performance headphone solution.
ADAU1778 ANC SoC
Discussion on active noise reduction technology in open sound field
If the active noise reduction technology is classified according to the different scope of action, the noise source and noise reduction point of action are single, and wearable devices, such as noise-cancelling headphones, are required to reduce noise, which belongs to single-point active noise reduction. With the help of wearable devices, it belongs to the active noise reduction of the open sound field. The 3D space active noise reduction technology not only requires excellent active noise reduction algorithm skills, but also requires a profound acoustic theoretical background to analyze, simulate and reduce noise in the 3D space sound field, so as to achieve active noise reduction in specific areas under the premise of non-wearing. , and then greatly expand the scope of application, so the technical difficulty is greater.
At present, the application of 3D space active noise reduction technology is relatively mature in the noise reduction of automobile engines. However, due to the fixed and low frequency of engine noise, noise reduction is relatively easy. In addition to noise, there are tire noise, wind noise, and external environment noise. At this stage, cars mainly use the more traditional technologies of vibration reduction, noise reduction, and sound insulation to reduce noise. A further technology is the use of ANC in-car active noise reduction technology. It needs to rely on software to drive, and then use the in-vehicle microphone to collect noise samples. After the system analyzes the noise spectrum, the in-vehicle speakers play sound waves with the opposite phase and the same amplitude as the noise to achieve the purpose of canceling the noise.
Recently, ADI and Hyundai Motor Co., Ltd. jointly launched the industry’s first fully digital road noise reduction system, which is the first system that can significantly reduce noise in the car cabin. Noise Active Noise Control) systems face multiple challenges. The RANC system is based on the existing ANC technology, and on this basis, the function and signal transmission speed are optimized with the aid of the A2B bus. Generally, tire noise or engine noise can enter the cockpit in about 0.009 seconds. Based on A2B, a delay of up to 2 clock cycles (50Mbps) can be guaranteed. Due to its optimized calculation and signal transmission speed, it only takes 0.002 seconds to analyze noise and generate reverse sound waves produced by a digital signal processor (DSP), which was a challenge for traditional buses of the past. RANC can accurately analyze and calculate the noise generated by the front and rear seats in the vehicle through special signals and sensor positions, and can reduce the noise in the car by 3dBA, which is also the core of RANC technology – don’t underestimate 3dBA , in the field of sound pressure, 3dBA is equivalent to reducing the noise in half.
Hyundai RANC System
The figure below is a schematic diagram of the ADI active noise reduction technology in the car cockpit. The core of the active noise reduction controller is still the audio processing DSP. ADI envisages that in the future cockpit, different seats in the car can form independent sound zones, and the audio content heard in different positions is also different, and there is not much interference between each other – such a scene also requires audio processing very much DSP. Perhaps in the future, traditional powerful cassettes will be added to the DSP chips of ADI audio processing to better process corresponding sounds in different application scenarios.
Schematic diagram of ADI’s active noise cancellation technology
In addition to the application in the field of car cockpit, in today’s comprehensive upgrade of consumption, there is a strong demand for noise reduction technology in the field of home appliances, but the application and layout of the application is still a blue ocean. As the main focus of the household market, various noises such as mixers, vacuum cleaners and toasters are annoying to many consumers, so they are willing to pay more for household appliances with noise suppression functions. At CES2020 not long ago, ADI demonstrated the active noise reduction function of household appliances (coffee machine) based on ADAU1452 audio processor, which can achieve 10dB(A) noise reduction effect. Such solutions can also run on household appliances that generate loud noises, such as soymilk makers, so that uncomfortable noises can be eliminated from the home environment.
ADI Demonstrates Noise Suppression from Home Appliances Using Its SigmaDSP at CES 2020
Summary of this article
Nowadays, with the increasingly fierce competition in electronic products, sound quality experience has gradually become an important factor in product competitiveness, which has also prompted the widespread application of active noise reduction technology. As more and more partner products based on ADI ANC solutions are implemented in multi-scenario applications, it is believed that active noise reduction technology will have more room for imagination in the future.