Automotive Acoustics: How to Address Complexity
The push to solve modern cars’ complexity challenges is increasingly focused on software, and this includes the intricacies built into acoustics design and performance. How can automakers address these challenges?
This is a critical question since automotive acoustics systems are subject to ever-increasing sophistication and performance requirements. In addition, audio is constrained by the laws of physics. It requires precise and consistent results with low latencies, and automakers must meet these demands with hardware that can operate reliably and within cost constraints.
Vehicle Acoustics Challenges
When you think about the sound coming from the exterior of a car, the first thing that might come to mind is the pounding bass from a vehicle next to you at a stoplight. But there’s more to exterior sound than noisy neighboring cars in traffic.
There is a multitude of components complicating the design of automotive audio systems, creating a new class of obstacles. However, new answers to these challenges are emerging, as well.
This article explores how automakers are finding ways to satisfy myriad audio feature demands — often with competing requirements — while leveraging their existing hardware and software configurations.
Car Exterior Acoustics Factors
There are at least five different types of sounds making their way into the cabin of a vehicle, all competing for the driver’s attention. (Ironically, this list does not include music or other entertainment programming intentionally chosen by the car occupants — the one source that most people associate with automotive acoustics). Automakers are increasingly seeking to manage these various audio sources by incorporating the following types of solutions into their automotive designs.
1. Engine Noise Reduction
While hearing the engine might be appropriate for a muscle car, luxury brands often want the car interior to be as quiet as possible. One important means of accomplishing this goal is with active noise cancellation, which works much like noise-canceling headphones but on a larger and more complex scale. This uses the engine’s known sound profile and pumps sound with an opposite phase into the cabin to remove or reduce engine noise for the comfort of the driver and passengers.
2. Engine Sound Augmentation
While electric vehicles (EVs) and hybrids may be producing audio to mimic an engine sound to alert pedestrians, the same can be done for subtly adding the external sound of an engine inside the car. In the pursuit of increasingly efficient gasoline engines, cars are being built using fewer cylinders (or none, in the case of EVs). Some designs feature cylinder deactivation, where some temporarily stop firing, eco-smart on/off engines, and turbochargers. These can periodically change the sound of an engine (or eliminate it), which can be disconcerting to the driver. Engine sound augmentation adds some of the missing audio back in to make a gas-sipping engine sound more like its less-efficient counterparts, giving the driver familiar audio cues.
3. Road Noise Reduction
Similar to engine noise reduction, some automakers may wish to further silence the interiors of their cars by removing road noise created by tires on pavement or environmental noise, like construction zones or even the pounding bass from our booming next-lane occupants. These typically require a microphone to sample the sound and then, acting similarly to engine noise reduction, they create canceling audio waveforms for the internal audio system to playback.
4. Pedestrian Awareness
Purely electric cars — and hybrids when running on electric power — make very little noise. This quiet is nice for the environment and interior occupants but can reduce pedestrian and bicyclist safety. Distracted pedestrians may not be aware of a vehicle operating so quietly until it’s dangerously close, and then they may be startled and move unpredictably. This is why EVs and hybrids often emit an engine-like sound, alerting nearby pedestrians, bicyclists, and visually disadvantaged people to their presence.
5. Reverse Alerts
What sound is ubiquitous on construction sites? The infamous “beep-beep” backup sound. Something similar is coming to many new cars since it alerts those around the vehicle that the driver may not see them. These alerts don’t always have to be loud and intrusive. Gentler-sounding or even “white-noise” alerts are becoming popular options for passenger vehicles.
Car Interior Acoustics Factors
The modern car interior has a few sound sources of its own. These may be more familiar than the audio sounds of the exterior but are equally complex to manage and achieve precise specifications.
1. Head Unit
Also known as the infotainment system or center stack, the head unit is often the heart of what most people think of for car audio. It contains the stereo — the first “in-vehicle” sound source — that for some customers, is still the most important. It also includes several forms of media playback (streaming, USB, Bluetooth®, and on-device media), Android Auto™, and Apple CarPlay®. Still other in-car audio comes from navigation system prompts, infotainment system UX sounds, alerts, turn signals, and more.
2. Hands-Free Calling
A good hands-free system for the car requires excellent echo-cancellation and remote-end noise reduction; a premium one also uses a microphone array and adaptive beamforming to focus in on the person talking, and to eliminate as much of the vehicle’s ambient noise from the call as possible.
3. Speech Control
Speech control has similar requirements to hands-free, although with wake-up words it must be running continuously. It also must be routed to different places — an on-board speech engine, off-board recognizer, a phone-based voice assistant, or even a combination of these.
4. Alerts and Warnings
Standard alerts — like door or trunk ajar, engine still running, or passenger seat belt disconnected — also need to be handled by the audio system, often requiring input from several different modules. In addition to these alerts, a wide variety of sounds related to ADAS (Advanced Driver Assistance Systems) are being added, including forward collision warning, lane departure chimes, or blind spot detection alerts. Increasingly, sounds for events like turn signals are also created through the audio system, instead of from a dedicated “clicker” relay.
5. In-Car Communication
This feature is most noticeable when someone in the front of the car is trying to talk to someone in the back seat, especially in louder or larger vehicles. Audio systems with this feature isolate and emphasize the speech between front and rear seat passengers. This eliminates the need to raise one’s voice, or worse turn their head around to talk to the passengers thus taking eyes off the road. Essentially, the phrase, “What did you say?” gets eliminated.
Combined Sound Sources in Automobiles
The fundamental challenge of merging these sound sources arises from too many systems in play, all of which have demands on the audio system. In current car designs, most of these audio sources are individualized, and completely independent modules. That means the audio waveforms being played back through the speakers, and being sampled by microphones, are not controlled by a single entity — in effect, these multiple audio components are battling it out in the acoustical space of the car. Domain controller and zonal architectures consolidate ECUs, combining some of the systems to run on the same silicon, yet they are still unaware of each other.
An uncoordinated audio system will deliver a poor audio experience. Unsynchronized audio inputs and outputs with competing needs can introduce a host of issues, like saturated mic levels, far-end echoes, audio glitches, distorted speech, induced noise, howling feedback loops, stuttering audio, inaudible alerts, and poorly performing speech recognition. All of these things can also potentially hamper driver perception and performance, and ultimately, affect safety.
Addressing Vehicle Acoustics Complexity
Methods of solving the vehicle acoustics complexity problem can be simply stated, but difficult to achieve. An increasing number of automakers find that the solution lies in centralized control that integrates and orchestrates holistic vehicle audio, and audio systems.
Why is this so challenging? Part of the problem is that there are typically multiple vendors providing different components of the system. There are multiple SoCs (systems-on-a-chip), DSPs (digital signal processors), and operating systems that even a centralized audio controller must run on. It must be aware of a wide variety of audio uses, and manage the audio resources intelligently, while also prioritizing them for sound quality — but not at the expense of safety. And it must have consistently low latencies for the most demanding use cases, while being able to accommodate playback streams from slow and non-deterministic audio applications.
Taken as a whole, that’s a tall order for an overall audio system, and very few technology platforms can measure up. In our next post, we will examine some specific audio technology solutions that can help with these challenges.
About BlackBerry QNX Acoustics Management
The QNX® Acoustics Management Platform (AMP) 3.0 from BlackBerry is a breakthrough in automotive software. For the first time, automakers can design and manage the total sonic experience in their cars with a pure software solution designed to run on general-purpose application processor cores — saving bill-of-material costs and cutting time to production, while delivering new features and uncompromising sound quality.
About Bradford Hamme
Bradford Hamme is the Principal Solutions Architect, Global Acoustics at BlackBerry QNX.