Thought Leadership

Standardizing the Immersive Audio Playback Chain

Immersive Audio Listening Room at Genelec: Customized room for listening to spatial audio

Immersive Audio Listening Room at Genelec

If you follow my posts, you’ll know that spatial audio measurement is a big research area for us right now. As immersive audio takes off, it’s important that designers of spatial audio systems have the tools they need to accurately measure spatial sound characteristics such as localization and envelopment. This will enable consistency in playback so that artists and mixers know that the effects that they are creating sound as they intended, no matter what the consumer’s playback equipment.

To complicate the issue, having designed the playback system, manufacturers also need to take into account the myriad ways in which their customer may configure their speakers to ensure consistent reproduction. This is no simple task when room acoustics also comes into it and few consumers have a perfect listening space.

While we are some way from having universal measurement techniques and standards, I witnessed an interesting insight into how Genelec is addressing the issue of customer configuration at the AES/ASA/BAS Boston chapter meeting at their facility in Natick earlier this week.

First we received a demonstration in their newly-configured immersive room where they demonstrated several soundtracks. This included correlated and uncorrelated pink noise at low frequencies to illustrate bass reproduction. They also played a couple of musical pieces including the musical score from a video game (which was surprisingly impressive) and a piece of Indian music. These were both very immersive, with sound coming from multiple directions. What I found interesting about this was that in the 9-seater listening room, there was really only one sweet spot or seat where you received the full impact of the immersive experience. The effect in the other seats was not uniform and depended on the seat’s position relative to the center spot. This will certainly present challenges to sound designers!

In a separate room, we saw how Genelec helps their customers ensure that their equipment is correctly configured. This was impressive too! Their bespoke software uses a microphone and network adaptor to make measurements in the room and upload them to a server. The speaker-room interactions are diagnosed, and their software returns a comprehensive report including frequency response, time response and time-frequency analysis including wavelet analysis. It also provides an electronic file that equalizes and time-aligns the speakers to compensate for the room characteristics and exact speaker placement. This ensures that Genelec’s customers are hearing the sound as they intended, regardless of their room configuration.

This is a great start, and it’s encouraging to see spatial audio playback system vendors following through to ensure the end user’s experience is as intended. However, this is only one part of the puzzle. There is still a need for the industry to agree on useful metrics that allow manufacturers to design and evaluate their systems to Dolby Atmos and other spatial audio specifications. This will allow the creative effects of spatial audio to transcend individual manufacturers and allow consumers hear exactly what the recording engineer intended, regardless of their chosen brand of playback equipment. If you make spatial audio playback equipment, what metrics do you think show the most potential for evaluating spatial sound effects? We’d love to hear from you.

The Missing Measurements – Challenges of Measuring Immersive Audio

The University Atrium and Presentation Space that was Simulated in the Immersive Listening Room (Photo courtesy of Acentech)

Earlier this week I attended the AES Boston section meeting at Acentech’s state-of-the art facility, lured by the promise of a demonstration of their 3D acoustic listening simulation. I was not disappointed! After some drinks and conversation with other attendees, we broke into smaller groups to experience their immersive listening room. Although only the size of a large conference room, this room simulates much larger spaces such as lecture halls, restaurants and offices.

We listened to a simulation of a University atrium and presentation space. There was a dining space on a balcony above it, and offices and classrooms above and behind that. We heard how it would sound both with and without diners during a presentation, and if you closed your eyes it was easy to believe that you were actually there. This impressive auralization was created by first recording a presenter in an anechoic environment, then applying sophisticated predictive models to apply reflections, reverberations and background noise to account for the room configuration and construction materials. It was then reproduced in the immersive room on an Ambisonic playback system. This model permits not only evaluation of  architectural features, but also experimentation with different materials for walls, windows, furniture etc. Architects, designers and sound consultants can evaluate and adjust the acoustics of a room at the design stage, ensuring acoustic perfection in the finished product.

What I found surprising was the lack of feedback to the model based on real measurements. It seems that there’s a prime opportunity to make actual measurements in the room once it is built, and compare this real-life data to the model. This was also apparent when I spoke to another attendee, a recording engineer, about mixing in Dolby Atmos. We discussed how he could master something until it was perfect on his Dolby Atmos system, but there was no way of knowing whether other listener’s Dolby Atmos systems would reproduce the sound in the same way he intended.

Spatial audio measurements are still in their infancy, and they are a complex combination of perceptual measurements such as localization, intertwined with room acoustics. Until we devise reliable and accurate ways of measuring spatial audio, we have no way of measuring room simulations to compare them to actual measurements, and no way of comparing the fidelity of various Dolby Atmos playback systems. This is a source of frustration for many product design engineers who are accustomed to having good measurement data to drive their product development.

Recently, I’ve been investigating how a binaural head perceives virtual source location and envelopment, and we’ve developed some rudimentary ways to measure sound localization and envelopment using interaural level difference and interaural cross-correlation measurements with a head and torso simulator. What are your thoughts on spatial audio measurement and what measurement techniques and metrics you are working on? Let me know in the comments and please reach out for me if you’d prefer an offline discussion.

Learn more about Acentech.

Learn more about stereo soundfield measurements for quantifying sound localization and envelopment.