Have you ever been bothered by the sound of your neighbor building something? What about the sound of insects on a summer night or the roaring of passing cars? Our ears are constantly being bombarded with sounds no matter where we are. Over time, these sounds can damage our hearing and can even affect vision in severe cases.
Most people try to block out annoying noises by buying headphones with better sound insulation or increasing the volume on their devices, but both options can also damage hearing. What else can you do? Active Noise Control (ANC) provides a solution. While ANC utilizes advanced technology, it has actually been around for a long time. It matches one sound wave by generating a second sound wave with the same frequency but opposite amplitude to achieve noise reduction or elimination. In the past, this technology was mainly used for specialized purposes, such as aviation systems, high-end vehicles, military equipment, or high-end professional headphones.
However, the continuous development of technology and the constant expansion of the consumer market have led to widespread adoption and adaptation of ANC technology for everyday life.
Everyday applications for ANC technology
ANC may be an unfamiliar concept for most people, but it is actually an important part of our everyday life. Headphones, cars, and many home appliances use ANC technology.
1. Earphones / Headphones
ANC is gaining more and more popularity among younger generations because its noise reduction technology drastically improves the user experience. Most people have different sensitivities to sound quality, so earphones and headphones ranging from 20 to 200 dollars often fail to demonstrate any improvement or real difference to consumers. However, ANC technology creates a clear difference in quality. In a noisy city, wearing ANC headphones is like having your own small world. Users are free to listen to songs, watch videos, or receive phone calls without interruptions or distractions.
ANC headphones employ a simple process to achieve noise reduction. First, the headphones receive an outside sound wave, and the sensors embedded in them convert the sound into an electromagnetic wave. Then the noise reduction system generates a sound wave of the opposite amplitude to reduce or even eliminate the noise.
There are currently a variety of ANC headphones on the market, and several famous brands, such as Sony and Bose, offer different models with ANC.
For instance, Sony offers a diverse range of unique headphones to meet consumer needs for a variety of scenarios. Bose headphones even redefine noise reduction with their advanced technology. Specifically, Bose Noise Cancelling Headphones 700 offer various options for noise cancellation with levels from 0-10. Level 0 enables users to deactivate ANC function to listen to both their content and ambient noises, such as people speaking or cars honking. Once users no longer need to listen to ambient noises, they can return to their own private world by switching to level 10 for complete noise cancellation.
2. Cars
Do cars need noise reduction technology? Of course. There are basically four sources of noise for cars: the engine, tires, air, and resonant vibrations from the car body. Many high-end cars combine cotton insulation, double-pane windows, and quiet tires with ANC technology to minimize noise.
Cadillac is a leader in applying ANC technology to cars. It prioritizes a quiet in-vehicle atmosphere as its most basic requirement for establishing cars as a “third space”, or a place of rest outside of home and work, during travel. Cadillac proved its commitment to this concept as early as 2013 with the launch of its XTS luxury sedan equipped with the premium Bose 5.1 surround sound system. The system collected noises through microphones or sensors in different parts of the vehicle, including the acceleration and vibration sounds from the vehicle body. It then actively played sound waves with opposite amplitude with its Digital Signal Processor (DSP) to cancel out the sound wave of the noise.
Figure 1. Active Noise Reduction in Automobiles1
The models following the Cadillac XTS, including the Cadillac CTS, CT6, and XT5, were also equipped with ANC technology. However, ANC is not limited to Cadillac, and use of ANC technology is now widespread among different car companies and models. Car models with high-performance ANC include Honda Accord, Ford Mondeo, Buick Envision, and more.
3. Homes
Increasing living standards are driving a growing demand for indoor noise reduction. Ambient sounds outside of windows, the activities of neighbors, and the operation of home appliances can create a high level of noise pollution and adversely affect occupants. Purchasing appliances with ANC technology is currently one way to minimize such noise pollution. However, developing ANC for 3D open sound fields to reduce noise pollution will be the most effective solution for controlling indoor noise in the future.
Current ANC technology can manage noise reduction frequencies of about 50Hz-1,000Hz. The noise reduction range can also manage noises with medium and low frequencies, such as noises from tables, chairs, and footsteps in the upstairs room. This technology provides several advantages over traditional soundproof insulation. It advances technology and develops environmentally friendly practices by:
• Reducing the use of thick and heavy materials for less pollution.
• Simplifying installation, maintenance, and replacement.
• Increasing the efficiency of noise reduction.
Mainstream technologies for noise reduction
The three most essential components of ANC are ADC, DSP, and DAC. The Analog-to-Digital Converter (ADC) converts environmental sound waves into digital signals. Digital signal processor (DSP) analyzes the signals to generate opposite digital signals. Finally, the Digital-to-Analog Converter (DAC) converts the digital signals back into sound waves.
Figure 2. Flowchart depicting Digital ANC process2
Because previous generations of DSP chips lacked the power to support complex computing in real time, analog ANC was the only option on the market. However, the rapid development of DSP chips has helped create three types of ANC: feedforward ANC, feedback ANC, and hybrid ANC.
Feedforward ANC places a single microphone on the outside of the earpiece. It receives an outside sound signal, transmits it to the ANC hardware, and cancels the noise before the user hears it. However, using a single microphone on the exterior increases exposure to background noise and makes achieving high sound quality difficult. As a result, the superior potential of hybrid ANC for noise reduction is attracting an increasing amount of attention. Hybrid ANC places a microphone on both the interior and the exterior of headphone earpieces to reduce sensitivity to background noise and suppress noises more effectively.
ADC, DSP, and DAC are all indispensable in ANC technology. The ADC converts the environmental noises into digital signals. The DSP uses advanced algorithms to reduce sound delay. Finally, the DAC creates an isolated sound environment in seconds to create an atmosphere of profound quiet.
Future trends for ANC semiconductors
In 2020, the substantial sales growth of the True Wireless Stereo (TWS) headphones helped drive the development of ANC technology. Many IC (integrated circuit) design firms have already made several breakthroughs in ANC technology. Design houses such as ADI, ams, and Unisoc are competing in the ANC market.
ANC semiconductors are adapting to the bigger market by becoming smaller and lowering power consumption. Many IC firms are prioritizing smart technology in developing methods to align ANC semiconductors more closely with technological evolution in the future. ANC products can employ smart technology with optimized noise reduction models and algorithms for greater adaptability to diverse application scenarios. These products will eliminate manual noise reduction configurations and reduce power consumption with smart technology.
The intellectualization of ANC semiconductor requires a lot of big data processing and machine learning, and it is known that semiconductor memory plays a vital role in the big data processing. It is believed that the ANC industry along with the rapid development of semiconductor memory can become more intelligent and being applied to more applications in the future. SK hynix’s DRAM and NAND flash memory products will contribute to the development of this industry as well.
Companies are also trying to advance integration across automotive, industrial, construction, and other sectors to incorporate semiconductor chips into a variety of processes and environmental improvement efforts. Their end goal is to build an effective system for noise reduction in a unified 3D environment.
The future possibilities for ANC technology are endless. It can be combined with cameras to intelligently monitor noise pollution from vehicles on the road. Cars, trains, and planes can use ANC technology to provide quiet and comfortable trips. Construction noise pollution can be dramatically reduced to benefit nearby residents, and construction sites can operate longer with increased productivity. Finally, ANC technology with smart features will redefine how we live by enabling us to enjoy the sounds of nature.
1Reference: https://www.eefocus.com/automobile-electronics/463870?utm_source=newsletter&utm_medium=email&utm_campaign=mar_new_article
2Reference: https://www.edn.com/a-perspective-on-digital-anc-solutions-in-a-low-latency-dominated-world/
