Hyundai and Analog Devices Team Up for “Industry’s First All-digital Road Noise Cancellation System”January 29, 2020 by Robin Mitchell
Analog Devices' Automotive Audio Bus (A2B) technology uses a daisy-chain topology and combines power and data into a single twisted pair.
Hyundai Motor Company has announced that, in partnership with Analog Devices, it has spearheaded the "automotive industry’s first all-digital road noise cancellation."
Automotive Audio Bus (A2B) technology. Image used courtesy of Analog Devices
Hyundai has attributed the success of this system, in part, to Analog Devices' Automotive Audio Bus (A2B) technology.
What is Noise Cancellation?
Noise cancellation in vehicles is the process whereby local audible noise is canceled. Such sources of noise can include fans, motors, and machinery.
The process in which noise is removed falls into two categories: passive techniques and active techniques.
Just like in electronics, passive noise removal uses the inherent properties of a material to reduce noise without consuming energy. Active noise removal, on the other hand, uses complex circuitry and mechanisms that consume energy to remove noise.
A2B transceivers distribute audio and control data together with clock and power over a single twisted-pair wire. Image used courtesy of Analog Devices
Examples of passive noise removal techniques include sound-proofing foam, spring beds, and acoustic cavities, while active noise cancellation often utilizes inverting sound waves.
What is RANC?
RANC stands for Road Active Noise Cancelation and concerns the removal of road noise inside a vehicle using active methods.
Some cars deploy passive solutions (such as exhaust mufflers) to remove resounding noise inside the vehicle, but these methods can only go so far.
For example, when wheels make contact with the road, they produce noise directly transferred into the vehicle's chassis since the wheels have a solid connection using the axel, bearing, and fittings. Noise like this can be difficult to remove using standard passive techniques.
This is where Hyundai's RANC comes in.
Researchers testing Hyundai's RANC technology. Image (modified) used courtesy of Hyundai Motor Company
RANC uses the standard method of active noise cancellation whereby the noise from the road is recorded using an external mic. Then, the exact same sound is played inside the vehicle from built-in speakers.
However, the sound from the speakers is inverted and played in phase with the noise as it reaches the speakers, causing the sound waves to cancel out.
Most active noise cancellation systems also include internal microphones to measure the noise-canceling effect in a negative feedback loop. That way, if the inverted wave is not directly in phase, it can be adjusted until it is.
While in principle the active noise cancellation technology sounds simple, there are several problems that vehicles face when implementing such a feature.
The first problem relates to weight efficiency. Practical noise removal systems require speakers in multiple positions around the vehicle, which requires a large number of cables going to each speaker. This increase in cabling would increase the overall weight and therefore reduce fuel efficiency.
Another problem faced with such technology is the need for many sensors to communicate together and transmit audio data faster than the sound wave can propagate. Noise cancelation only works when the noise can be recorded, processed, and emitted before the original noise reaches the speaker.
This problem is potentially amplified in vehicles as sound travels faster in solid objects than it does in air. This entails that each noise-canceling speaker would need a built-in microphone and amplifier that would report back to an audio processor.
To combat these issues, Analog Devices developed a communication protocol called Automotive Audio Bus (A2B), which works very similarly to I2C, but with a few key differences.
The first major difference between A2B and I2C is that A2B combines power and data into a single twisted pair whereas I2C uses separate power and data lines.
A2B Active Noise Control (ANC) and Road Noise Cancellation (RNC) technology. Image used courtesy of Analog Devices
Since A2B uses a daisy-chain topology, a number of speakers can be connected serially on the same twisted pair without the need for a twister pair for each speaker in the system (most likely in a similar fashion to WS2811-based LEDs).
A2B also does not require the use of a shielded cable, which further reduces the cost and weight of implementation. The maximum bandwidth is 50Mbps, which offers support for 32 upstream and downstream audio channels.
Analog Devices claims that its A2B technology may decrease audio cabling systems by up to 75%. The technologies' high bandwidth in conjunction with its daisy-chain feature makes way for practical active noise cancellation in vehicles.
Analog Devices asserts that their configurable evaluation boards allow developers to meet audio design requirements. Screenshot used courtesy of Analog Devices
A2B can easily be applied to most audio applications outside of automotive noise-cancellation as well. Relevant applications may include those that require low-latency audio, such as hands-free speech, voice recognition, home theaters, and intercom systems.
Designing a noise-cancellation system can be a complex task. If done incorrectly, it can create undesirables results, such as high-frequency audio hiss. The need for many sensors and speakers can dramatically increase the number of cables required in a vehicle, which increases the weight and complexity of the overall construction.
A2B offers a real solution for vehicles that need to implement Road Active Noise Cancellation, where high-speed, low-latency audio data is required to be processed.