The Future of In-Car Audio Measurements

July 11, 2024. A couple of weeks ago, I attended the AES Automotive Conference in Gothenburg. While I expected in-car audio measurements to be a discussion point (after all, that’s why I went), I hadn’t counted on it being such a strong focus of the show, and I was excited by the incredible collaborative efforts that are happening to bring the world better quality sound in cars.

Much of this can be attributed to the AES TC-AA white paper on proposed measurement techniques for automotive audio that was published for review last year. This white paper was a collaborative effort between a worldwide group of engineers that included car manufacturers, car audio system designers and measurement experts. Under the leadership of Jayant Datta, we devised and documented methods for measuring frequency response, Max SPL and impulsive distortion in cars. The white paper outlined an entire proposed standard from physical setup such as microphone positioning, to controls (e.g. volume), test signals and analysis methods, and invited feedback and discussion.

Until a couple of weeks ago, we had received minimal feedback from the industry as a whole, to the extent that I sometimes wondered if it had been worth all the effort. This conference changed all that! I was pleasantly surprised with the number of people who showed up to see me demonstrate these measurements in a shiny new Volvo XC60 (Thanks Jonatan and colleagues for allowing me to use your demo car). Similarly, a good number of attendees showed up for our panel discussion on the paper, especially considering it was the last afternoon of the event and many had already left to travel home. In this session, Jonatan Ewald, Marco Olivieri, Jayant Datta, Stefan Irrgang and I explained the proposed standard and showed some results.

I was excited to attend paper presentations where our proposed guidelines were carefully followed when making measurements. A great example of this was a paper “An empirical evaluation of in-car acoustic measurements for the sport car scenario” from Ferrari  who presented some excellent research on making measurements in sports cars: a 4-seater luxury vehicle and a 2-seater track-oriented vehicle. There’s nothing like the combination of audio and fast cars to get my attention!

From the conversations I had with other attendees, it seemed that many had read the paper and experimented with the techniques and configurations we proposed. From the overall positive reception, it’s clear that we are working along the right lines, but there were many valuable suggestions for improvement. This includes more options for positioning the 6 microphone array – the arrangement we proposed doesn’t fit too well in those sporty Ferrari seats! We also learned that people want more distortion measurements. The impulsive distortion that we included is ideal for an end-of-line check to make sure there are no rattling loudspeaker parts, but several manufacturers expressed a desire to measure other types of in-car distortion, for example Max SPL vs Frequency and THD. There was also some debate about correlated versus uncorrelated pink noise and how to measure accurately at low frequencies.

The white paper does not specify the method for getting the test signal into the car, leaving the user open to use Bluetooth, USB stick, memory card or other methods. Bluetooth is a popular choice due to its simplicity. However, it is apparent that despite its many advantages, consistent and reliable Bluetooth connections are more challenging than you would think.

The feedback we received at the conference made it clear that the standardization we are working towards is much needed, and could be considerably expanded to include more measurements. One attendee, for example, was particularly interested in expanding it to also cover measuring headrest speakers!

This brings me onto the second focus of the show – spatial audio. Cars are being built with more and more speakers in varying locations such as in the ceiling, headrests, and more in support of spatial audio and sound zones. Pretty much every manufacturer now supports Dolby Atmos playback, but measuring it accurately is a challenge that most automotive manufacturers have yet to solve. Infotainment designers strive to re-create the sound of a home-based system in the car, but most are currently tuning by ear, which is slow and inexact. Many are using inexpensive room acoustics software which requires manual operation and real time data analysis. While this works, it is also very time-consuming. More scientific methods for measuring spatial audio are in their infancy, but being developed rapidly by test and measurement companies, automotive manufacturers, and even Dolby themselves. I have a suspicion this could be a topic for a future AES Automotive conference. Stay tuned!

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