Hyundai's noise reduction technology brings an immersive cockpit experience

Next time you're driving, turn off the radio and listen. If you're in a typical consumer car, you've probably noticed a noticeable amount of noise inside your car. Whether it's caused by the engine, the tires, or the wind, these annoying noises can cause driver fatigue and compromise safety on long trips.

Previously, most automakers used passive sound-deadening materials to help with noise reduction. However, this added weight to the vehicle, which in turn increased fuel consumption. So, manufacturers borrowed active noise cancellation (ANC) technology from high-end audio noise-cancelling headphones and deployed this technology in millions of cars. While ANC is effective in eliminating the narrowband engine noise of the vehicle, it does little to suppress the broadband noise (road noise) generated by the tires.

At a joint technical seminar hosted by Analog Devices, Inc. and Hyundai Motor Company (HKMC), two leading companies discussed the issue of road noise reduction. ADI is a technology company that provides a full range of solutions and is good at solving difficult engineering problems. As a pioneer in the automotive industry, Hyundai Motor wants to distinguish its brand and develop technology that can significantly reduce noise inside the car.

The two teams worked together to deploy the industry's first fully digital Road Noise Active Noise Control (RANC) system. The challenge was to implement RANC in a practical and production-friendly way. In early 2020, the groundbreaking RANC system was accelerated into mass production and used in Hyundai's flagship GV80 car.

And this is just the beginning. Hyundai is looking to forge a path forward – one that goes beyond noise cancellation technology to deliver a more immersive, entertaining and high-quality audio experience across its entire automotive lineup, taking into account both the driver and passengers.

Overview

Company: Hyundai Motor Company is committed to providing human-centric, eco-friendly technologies and services that lay the foundation for more convenient, comfortable and safe automotive operation.

Applications: Leverage ADI's Automotive Audio Bus (A2B®) technology to implement basic audio connectivity and infotainment application functions.

Challenge: Bring the industry’s first fully digital road noise cancellation system to market while ensuring it is affordable, less complex, lighter, and accelerated to mass production.

Goal: Develop audio connectivity and infotainment applications for the entire automotive product line. Develop a more dynamic automotive experience.

Reduce noise

In the past, to reduce noise inside the car and make the car feel more premium, automakers would add sound insulation barriers in all possible places (floor, fairing, etc.). When lightweight materials were invented, they just added a lot of dampening effect, and then affected fuel efficiency due to the added weight. So they turned to a simple analog technology - active noise reduction, which was first used in the 1950s to reduce the deafening engine sound in the cabin of helicopters and airplanes, and later widely used by the headphone industry.

ANC is a simple and brilliant solution that can cancel out narrowband noise (not just suppress it). Similar to ripples combining with troughs in a lake, ANC works by flattening or canceling out the sound waves.

Eliminating road noise is not actually aimed at achieving quietness, but rather at preventing noise from making drivers and passengers feel tired. According to 2021 U.S. Department of Transportation statistics, vehicle mileage in the United States is as high as 2.3 trillion miles.

How Active Noise Cancellation Works

ANC technology works in the same way as noise-canceling headphones, using software and components such as DSPs and microphones to measure and reduce noise. Microphones in the car pick up engine noise and transmit it to a digital signal processor (DSP), where the ANC algorithm processes it and then sends a reverse audio signal back through the speakers. The driver and passengers will hardly notice the sound of this disruptive interference, but it is enough to cancel out the engine noise.

The ANC app "listens" to unwanted external engine noise and then (A) plays a sound 180 degrees out of phase with it (B), so that the noise is "canceled" before it reaches your ears (C). Digital processing must be extremely fast to accomplish this task.

Limitations of ANC

ANC technology is only effective for predictable, constant, low-frequency noise, such as the narrowband noise of an engine roar. * Random, wideband noise, such as potholes, can seep through. Because the signal and calculation speed of ANC are not fast enough to react quickly enough to generate a reverse wave. Its software and hardware have difficulty processing the noise reduction process within 4 milliseconds. This is the time it takes for road noise to reach the passenger's ears. Hyundai is looking for a better solution.

*This disadvantage can sometimes be an advantage. Being able to hear car horns or fire truck/ambulance sirens while driving is very important. Since ANC only cancels out low-frequency continuous noise, these important non-ordinary high-pitched cues come through loud and clear.

Hyundai Motor technical team takes measurements during the RANC test

Collaboration and participation

Hyundai and Analog Devices have a long-standing relationship that dates back more than a decade, with Analog Devices providing Hyundai with digital signal processing (DSP) technology for its premium audio amplifiers as early as 2012. In the following years, the relationship quickly evolved to focus on Hyundai’s Road Active Noise Control (RANC) system.

RANC technology not only has low signal latency and fast processing speed, but is also more than four times faster than the speed at which noise travels from the road to the cabin. In just 2 milliseconds, RANC analyzes road noise and sends reverse sound waves through the car's stereo speakers, canceling out the noise before anyone in the car hears it. In tests, RANC can reduce cabin noise by half, or 3 decibels.

2 milliseconds is the time it takes RANC to analyze and invert the sound wave

The RANC system proposed by Hyundai Motor consists of four main components: accelerometer, processor, microphone and speaker.

Accelerometers are located near each tire and detect vibrations in the tire and suspension.

The adaptive controller's (DSP) proprietary algorithm cancels out vibration noise within milliseconds by sending equal-amplitude reverse sound waves through the speaker.

At the same time, microphones measure the sound inside the cabin, ensuring a precise noise-cancelling signal.

The speakers in the cockpit close the signal loop and interfering sound waves are reduced. As a result, the interior area around each passenger is quieter and the listening experience while driving is more comfortable.

In early 2015, Dr. Kang-Duck Ih and his team at Hyundai Motor’s NVH Research Lab were working on the RANC application algorithm. ADI worked with Dr. Ih and his team to launch a new series of Griffin DSPs (digital signal processors) to implement the RANC algorithm. While discussing the RANC architecture, ADI learned that Hyundai’s solution was based on traditional analog connections, which were too expensive to deploy. To deploy automotive road noise reduction systems across the industry, cost-effective, low-latency network technology is needed to efficiently connect the required input sensors to the DSP.

A2B Solutions

A2B is a low-latency, cost-effective unshielded twisted pair connection solution that replaces expensive and bulky point-to-point coaxial cables. In addition to providing up to 32 channels of audio, control and phantom power over the same cable, A2B can also optimize daisy-chain network topologies, further reducing the weight and complexity of the harness.

“We initially worked with the Hyundai team to introduce ADI DSP and AB technology and roadmaps. The challenge at the time was a practical implementation of a RANC system,” said Vlad Bulavsky, general manager of Automotive Cockpit Connectivity at Analog Devices. “After many brainstorming sessions, we came up with a practical and deployable RANC solution that leverages ADI’s AB, accelerometers, and Griffin DSPs to replace competitor processors for the next generation of Hyundai automotive products.”

Hyundai and Analog Devices have been collaborating on this solution from 2015 to 2016. In early 2020, the two teams successfully deployed the industry’s first fully digital road noise cancellation technology product on Hyundai’s GV80.

Hyundai GV80

A2B technology advantages: greener cars, better features, better design

AB daisy-chains multiple remote sensors for different applications, significantly reducing redundant cabling. As a result, the weight of the cable harness is significantly reduced, and the overall design cost and complexity (in terms of design, installation and maintenance) are reduced due to fewer cables.

“We have worked closely with Hyundai Motor Company to create a fully digital RANC system, leveraging our AB technology to reduce equipment cost, weight, and design complexity, thereby improving overall fuel efficiency and helping to address many of the challenges facing electronic RANC systems,” said Andy McLean, vice president of the Automotive Cockpit Experience Group at Analog Devices. “ADI’s collaboration with Hyundai Motor Company not only demonstrates the growing importance of AB technology, but also further enhances Hyundai’s market competitiveness.”

“RANC is a great example of an application that requires the use of a variety of different technologies to achieve an effective system solution,” said Vlad Bulavsky. “ADI’s DSP, A2B connectivity, accelerometers, and software IP work seamlessly together to provide a high-performance, cost-effective solution to a very challenging acoustic problem.”