Exploring the software-enabled transformation of car audio

November 08, 2017

Exploring the software-enabled transformation of car audio

There is no doubt that software continues to have a material impact on the features and capabilities of the automobile – be it enhanced safety, improved fuel efficiency, better-sounding entertainment, or autonomous driving. However, the match between promises and actual performance has historically been far from perfect.

The J.D. Power market research company conducts an annual survey of U.S. vehicle owners that addresses top complaints. The findings of the survey offer a window into where the gaps between expectations and performances exist. The 2014 survey ranked problems with voice recognition systems as, by far, the number one issue raised by U.S car owners. Other common complaints related to difficulty with Bluetooth connectivity and excessive wind noise.

Moving ahead to the recent 2017 survey, one would have expected most of these issues to be resolved. Interestingly enough, complaints related to voice recognition systems, Bluetooth connectivity, and noise from road and wind are still the most prominent! In fact, per the study, “the Audio/Communication/Entertainment/Navigation category continues to be the most problematic area, accounting for 22 percent of all problems reported – up from 20 percent last year[1].” Clearly, there is more work to be done.

Figure 1. Top problem areas from the 2017 Vehicle Dependability Study conducted by J.D. Power. Source: J.D. Power 2017 U.S. Vehicle Dependability Study.

It seems obvious that legacy approaches to address many of these issues have come up short. For example, traditional methods of adding more passive dampening materials to minimize external wind/road noise and make the interior cabin quieter can only do so much. Moreover, in addition to adding cost, passive dampening adds incremental weight, which has a negative effect on the fuel economy of the vehicle. Carmakers are turning to technology, especially intelligent software-driven solutions, to tackle these problems. Let’s look at the example of noise cancellation and how active, software-based methods offer an answer.

Transporting audio within the car

Although acoustics has long been a key automotive design consideration, interestingly enough most improvements to the in-cabin experience have centered on the overall in-vehicle infotainment (IVI) application. According to conventional wisdom, whatever worked for a better IVI experience was also deemed good enough for audio. This made sense since audio and video usually went hand-in-hand.

However, the emergence of acoustic-centric applications such as active noise cancellation (ANC), engine sound enhancement (ESE), vehicle alert systems (AVAS), and other technologies have more recently led designers to take a much closer look at audio technology on its own.

But first things first: a fundamental component to enabling these new audio applications is the underlying bus technology. A shift from passive to software-based approaches requires an advanced bus infrastructure for the efficient transportation of audio data. The Automotive Audio Bus (A2B) developed by Analog Devices is a relative newcomer, and more importantly the only bus exclusively dedicated to audio.

A2B: Digital audio over lightweight cable

A2B gives carmakers a cost-effective way to deliver multi-channel digital audio, control data, and power, all over the same lightweight unshielded twisted pair (UTP) cable. Cable and assembly costs for A2B systems can be up to 75x lower than analog alternatives, and the lighter weight can also enable lower CO2 emissions. A2B also includes system-level diagnostics and compliance with automotive electromagnetic compatibility (EMC), electromagnetic interference (EMI), and electrostatic discharge (ESD) standards. And with deterministic, low-latency performance (50 µs) and 50 Mbps bandwidth, A2B is well suited for high-quality audio and other applications, including infotainment and noise cancellation.

Figure 2. The Automotive Audio Bus (A2B) delivers multi-channel digital audio, control data, and power over a cost-effective, lightweight, unshielded twisted pair (UTP) cable.

A2B-based connectivity delivers many benefits, especially relative to traditional analog-based networking still in use in the vast majority of vehicles on the road. Thanks to phantom power and a single master/multiple slave line topology that supports daisy chaining of nodes, A2B systems eliminate the need for local component power supplies and control processors to manage software overhead. As a result, A2B provides an easy and efficient way to link a head unit to an array of speakers and amplifiers around the vehicle in a scalable daisy chain, which is vastly simpler than implementing a high-end sound system with many independent, point-to-point connections.

As is always the case, the popularity of an emerging technology is dependent on, and can also be measured by, the reception of early adopters and other ecosystem players. There are several examples of A2B industry adoption and ecosystem growth, most notably Ford's January 2016 announcement that it will use A2B as its primary infotainment network technology. A few months before that, German communications tech firm Peiker (since acquired by Valeo) announced new A2B digital microphones with transceivers built in, supporting both in-car communication and noise cancellation. And, from an ecosystem perspective, Mentor, a Siemens business, is among the first independent tool vendors providing critical A2B test support, including the A2B Analyzer System – the only third-party development platform engineered to help significantly reduce development time for A2B systems by speeding configuration and functional testing.

Leveraging active noise cancellation

Unlike passive noise cancellation, which uses physical noise dampening materials, active noise cancellation is implemented using DSP techniques. The idea behind active noise cancellation is quite simple – carefully-placed microphones pick up external noise, which is then processed and a 180 degree out-of-phase anti-noise signal is generated to cancel the undesirable noise. Active noise cancellation is already available in some car models, though it has generally targeted periodic, low-frequency engine noise. Although every engine is unique, the noise behavior is predictable and typically dependent on the engine’s performance (RPM). As a result, engine noise can be modeled to a fair degree of certainty and then subsequently dealt with.

But engine noise is only a part of the overall picture. The second, trickier source of noise comes from the road – broadband in nature, unpredictable, and almost impossible to model. Unlike engine noise, road noise also varies with changes in road surface. Most noise cancellation solutions available today only deal with engine noise and are an incapable of handling road noise. The issue of tackling road noise has gained even more importance with the emergence of electric vehicles (EVs), which feature electric motors instead of gasoline engines.  Although EVs produce no engine noise, road and wind noise must still be addressed.

Although fundamentally the premise of cancelling road noise is the same as that of cancelling engine noise, the complexity of the challenge requires additional components to reliably track and cancel noise on a real-time basis. A combination of carefully-placed accelerometers, microphones, and speakers work in conjunction to pick up road vibrations, process the resulting sounds, and then generate the required anti-noise directed at the car’s occupants. Proprietary, high-performance algorithms ensure fast convergence, resulting in rapid adaptation and responses to noise from changing road surfaces.

An even bigger challenge is how to deploy a cost-effective combination of microphones, accelerometers, hardware, and software to cancel the random broadband road noise. Until now, technical and cost challenges have prevented carmakers from offering broadband noise cancellation. However, the combination of A2B networking technology, powerful DSPs, off-the-shelf A2B-based components (accelerometers, microphones), and software IP are bringing the road noise cancellation solution significantly closer to reality. By offering deterministic latency, A2B is perfect for networking microphones, accelerometers, and other components.

Advanced active noise cancellation technologies such as Mentor’s broadband XSe Active Noise Control (ANC) solution have been designed to precisely tackle the dual problem of cancelling engine noise and road noise. Using the XSe ANC as an example, an advanced algorithm effectively cancels both engine and road noise to create an ambient environment within the car cabin. Quiet zones created around the driver and passengers cover steady state, dynamic, and non-periodic components of engine, transmission, and road noise without interfering with the enjoyment of music, the utility of audio-based navigation systems, or the sirens of emergency vehicles. High-performance solutions such as XSe ANC enable advanced functionality with minimal hardware components.

Somewhat paradoxically, other emerging audio applications involve sound enhancement for both driver enjoyment and safety. The controlled rumble of a high-end sports car engine, for example, is a big part of that car’s signature appeal, which is why that engine noise can be digitally enhanced and piped into the cabin via advanced tools for analyzing the transmission of sound and vibration in a car’s cabin. Other sound-generation applications include various acoustic alerts, from chimes that play when the car is started or when parking as well as other safety alerts that combine to form the car’s personality, brand identity, and thus its relationship to drivers and passengers. It goes without saying that it is desirable, or even a requirement, for these multiple audio applications to coexist on the same vehicle. Without an innovative software-based solution, this would not be possible.

Unleashing the promise of software-enabled car audio

With the availability of software-based noise cancellation and enhancement solutions, engineers have one more tool in their arsenal to tackle noise-related problems. But, as referenced, automotive audio system design has until recently been the domain of engineers focused on infotainment and head unit systems, while the challenges of reducing extraneous noise and vibration in a car are traditionally handled by an OEM’s noise, vibration, and harshness (NVH) team. Therefore, to gain maximum advantage from the move towards software-based acoustics solutions, carmakers and their suppliers will need to work across traditional organizational boundaries to unleash the true promise of software-enabled audio.

The automobile of the future is changing in profound ways, so it makes sense that audio is finally emerging from the shadows to take its rightful place as both a key enabler of new ideas, as well as a differentiator for carmakers. As these software-enabled solutions start to roll out in production vehicles on a consistent basis, one can expect to see customer satisfaction reflected in better scores in future surveys.

Anil Khanna is Senior Manager at Mentor, a Siemens business, responsible for the automotive audio business line. Khanna is based in Wilsonville, OR.

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1. Rayadmin. "Segments & Award Recipients." J.D. Power Cars. February 22, 2017. Accessed November 07, 2017. http://www.jdpower.com/cars/awards/Vehicle-Dependability-Study-%2528VDS%2529-by-Category/1882ENG.