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Perception of Stereo vs. Immersive Live-Sound Systems

David Kennedy • February 2020Tech Feature • February 10, 2020

Another January has passed and another NAMM Show is in the history books! While far from complete, show coverage (our in-depth NAMM report starts on page 14), I want to mention a few of the NAMM highlights that I noticed, included DiGiCo’s dramatic unveiling of the new generation of its Quantum digital console. While some loudspeaker manufacturers unveiled updated products, d&b showed the new A-Series — which now provides variable coverage angles. L-Acoustics also unveiled Kara II — giving it “four-in-one directivity.” The loudspeaker design geek in me appreciated the new and improved loudspeaker drivers on display from several manufacturers at the NAMM Show, including: 18Sound — they showed a new state-of-the-art AMT HF driver — while B&C, Beyma, Celestion, Eminence and Faital Pro all showed woofers with ever-increasing power handling. I also appreciated the excellent demos of immersive systems by d&b audiotechnik and L-Acoustics. And for me, a NAMM high point, was the Thursday evening Christian concert by Michael W. Smith, with the tribute that Yamaha did to his 35 years of writing and performing music on Yamaha keyboards and his dozens of music awards.

One of my New Year’s resolutions was to resume my continuing education in professional sound design, and one of the best ways to do that it is by attending AES seminars — now also available at the NAMM show. L-Acoustics personnel taught several informative AES seminars on array/loudspeaker technology. Etienne Corteel, PhD, of L-Acoustics, shared his considerable expertise with immersive systems, presenting a detailed and excellent seminar on the production and theory behind L-ISA. I was so impressed by the dozens of intuitive and well executed graphics that L-Acoustics created for their AES seminar, “Scaling from Pre-production to Live Performance with L-ISA Immersive Hyperreal Sound Technology,” that I asked them to share some of their graphics for this article, to help me explain the perceptual differences between stereo and immersive sound systems for live-sound applications.

But, before we dig deeper into the L-ISA Immersive Hyperreal Sound Technology, let me summarize my previous four months of FRONT of HOUSE articles on immersive sound. I will endeavor to wrap up immersive live sound this month, with a focus on the perceptual benefits of immersive live sound systems compared to classic stereo sound systems. Note: See the inset box on this page with links to each article.

‡‡         Flashbacks

In my October 2019 article, “Multi-Channel Arrays — Immersive is the New Surround” (bit.ly/MultArray1), I covered, with the help of our editor, the 80-year evolution of the many types of main loudspeakers, along with surround sound formats that are now becoming immersive sound. Included were the numerous varieties of LCR (Left, Center, Right) and 5-channel main loudspeakers as well as: the history of Dolby and THX in the cinema industry, the substantial improvements that Dolby Atmos brought to cinema and how premium dance clubs are starting to introduce immersive audio into their venues with Dolby Atmos Music. I noted how object-based immersive software allows designers and users more options to scale the numbers of loudspeakers, based on the budget, target SPL, the size of the venue, the amount of spatial resolution desired and amount of envelopment.

Some systems use dedicated DSP; others have their immersive software program running on a high-power Mac or PC with generic routers, while some vendors offer mixer control plug-ins. Immersive systems require considerably more speaker locations than before, yet the main arrays need not be as large as in a system with fewer arrays, and some platforms permit for system enlargement over time. We concluded with a debate on LCR loudspeakers vs. L/R line arrays with several leading live sound engineers.

In the November 2019 article “Multi-Channel Arrays: Immersive is the New Surround, Part 2” (bit.ly/MultArray2), I showed how and why live “surround sound” has become “immersive audio.” And, it’s coming on quickly — as an example, The Recording Academy changed its “Surround Sound” Grammy Award category to an “Immersive Audio” category. The focus was on a typical turnkey Immersive Sound system.

Nov. Fig. 1: In traditional sound reinforcement with left/right audio (shown on the left) a large proportion of the audience do not enjoy the benefit of true stereo image. On the right, with several speakers across the stage, audience coverage is much improved. As a result the “sweet spot” becomes a “sweet area” and walking the room, the image is consistent.

The Nov. 2019 article’s Fig. 1, from Martin Audio (above) showed much improved sound coverage of a venue from an immersive system.

Nov. Fig. 2 – Improvements in sightlines, traditional P.A. vs. Soundscape

Nov. Fig. 2, courtesy of d&b audiotechnik (above) showed sightline improvements to be had by using several smaller speakers.

Nov. Fig. 3 – Isometric view of d&b Soundscape immersive live-sound system with five main arrays (at left) and surrounds.

Nov. Fig. 3 showed an isometric view of a sample d&b Soundscape immersive loudspeaker layout with five main arrays and surrounds.

Nov. Fig. 4 – Block diagram of a typical d&b audiotechnik 3D immersive system for a live-sound application.

I also worked with d&b to show, in Nov. Fig. 4, a simplified block diagram that is typical of a d&b Soundscape system for a live music venue application.

Note these sound systems can provide from less than 180° up to 360° of immersion (with the option of overhead speakers). The article wraps up with a few leading sound consultants and several key manufacturers discussing various aspects of immersive sound.

One of my favorite quotes in that November issue came from noted FOH engineer Robert Scovill: “I think immersive stands to completely reshape — for the better — the immersive live-sound listening experience, not only for the listeners, but also the people mixing the events. With immersive, the massive improvement in overall intelligibility for the entire listening geometry, coupled with the power of the localization of ‘watching’ someone play, and having it sound as if the audio is coming right from where you are looking, can’t be underestimated. Over the years, we’ve become so acclimated to the shortcomings of stereo in a large space that we’ve lost sight of how good it could actually be in this type of format. And once you mix in an immersive setting during a live performance, and then go back to stereo, it just feels so inadequate for the job at hand. Immersive is here to stay, even though it’s going to take considerable time for it to be fully adopted for pop and rock music concerts. But for music and entertainment formats like performing arts centers and houses of worship, I view it as a ‘silver bullet.’ The improvement for the entire audience is far from subtle.”

December 2019’s article — “Computer Modeling of Immersive and Multi-Channel Arrays” (bit.ly/CompMod1) covered how turnkey immersive, LCR and stereo live-sound systems differ in cost, with sample models of sound coverage and max. sound levels. Certainly, audio imaging can be improved with the greater number of immersive arrays across a stage. Also, I wanted to inquire how half-sized line-arrays or point-source arrays can provide the same SPLs and distant coverage of large stereo line-arrays, and whether surround loudspeakers are always included.

Dec. 2019 graphics

I pointed out that at this time, L-Acoustics’ Soundvision software is the only modeler that can simulate the multi-array coverage of an immersive design (shown in Dec. Figs. 6 & 8). So, other modeling SW developers should consider adding a method to display directional realism with multi-channel coverage.

My conclusion? Although the term “immersive sound” allows for surround and overhead loudspeakers, surround speakers are not always needed or included. Immersive live sound is at least, if not more, about superior sound coverage, better source localization and time-alignment across a venue as it is about surround sound. The surround (and optional overhead) speakers can be added later, as some systems allow for gradual system expansion over time (to reduce initial sticker shock). The need for surround loudspeakers is dictated by budget, content/program, venue space and setup time limitations. For example, whether acoustic simulation is desired or if any sound localization is required around the listening area. Some immersive DSPs, are speaker-type-agnostic, thus are less confined to rigid speaker system geometries than spatial/immersive algorithms that some brands use.

My January 2020 article, “Branded vs. DIY Options for Live Immersive Sound Systems” (bit.ly/Brand-v-DIY), explained how there are several vendors of immersive sound programs, but that most of the currently available DIY immersive software programs are actually intended for the offline editing of immersive mixes and not yet proven for live sound. Fortunately, several makers of immersive systems are working to soon offer more optimized immersive mix software (with real-time editing) and intuitive control interfaces for the concert and church sound markets.

Jan. 2020, Fig. 3

On the hardware side, one option is to hire a sound designer and an integrator, who are expert in immersive systems design and installation, or work with a manufacturer (turnkey or a collaboration), who can design, supply and support a complete/turnkey immersive system. Jan. Fig. 3 showed Astro Spatial Audio’s simplified block diagram, representing an example of a collaborative (multi-vendor) approach to sourcing an immersive system. There are a wide range of immersive components and system approaches, with some proven to be much more reliable than others. Clearly, there are many different ways of creating an immersive production and sourcing an immersive system. So, as I explained, plan well in advance for immersive projects.

I also asked Terence Caulkins, PhD, acoustics and AV consultant with NYC-based Arup, to explain DIY immersive sound: “DIY solutions for immersive audio design have existed for many years, though until now, they were mostly used by a niche group of researchers and sound artists around the world. As mentioned in the October article, with today’s large tech companies pushing VR and AR, there are many solutions for immersive audio today beyond the solutions already mentioned above. In a large venue, live sound context, your main priorities should be the quality of sound produced by the sound system (timbre and time alignment), SPL, evenness of coverage over the audience area, latency of the live sound and stability of the system. All the rules of typical system design apply, including loudspeaker selection, room acoustic design and system calibration.”

Caulkins continued, “If you are bravely inclined to go with a fully real-time DIY immersive audio workflow on PC, it is good practice to have redundancy, with a second identical machine running the show and receiving all the same audio inputs and control cues as your primary PC. Whether or not you are pre-rendering your immersive audio, the simplicity of your user interface is a key factor in the live sound world. There is a lot of room for improvement on this topic in the DIY world, where the user interface design of many systems is exceedingly complex. The creation of simple, robust interfaces with easy to understand controls is a must, if DIY tools are to be adopted on big-venue production jobs, where engineers are working to satisfy the needs of big-name artists and executives, with little time for experimentation and/or improvisation. If some of the turnkey and DIY solution developers currently out there can work together and adopt the MPEG-H 3D format, it will pave the way for the standardization of immersive audio in the live-sound industry!”

Due to limited print space, the planned sidebar article on “PC Hardware Requirements for DIY Real-Time Live Immersive Applications” only appears at the end of the online article, as explained by both Caulkins and Hugo Larin of Flux Audio.

‡‡         Immersive Live Sound Production and System Design

Now, let’s look at some of the key graphics that L-Acoustics has shared from its excellent recent seminar on L-ISA Immersive Hyperreal Sound Technology. Other manufactures use a similar philosophy.

Fig. 1: L-ISA immersive live-sound system array layout

Fig. 1 shows the loudspeaker layout for a typical immersive system in a concert sound venue. The loudspeaker type and layout are critical in delivering a multi-dimensional/immersive experience. The loudspeaker layout looks much like a Dolby Atmos cinema loudspeaker layout, and since the typical concert sound venue is much larger than a typical cinema, the number of loudspeaker channels is greater and the loudspeaker types are typically line arrays, to provide the needed sound coverage/projection.

“We also use a higher-resolution frontal system,” says L-Acoustics’ Etienne Corteel. Most Dolby ATMOS systems will have only LCR for the frontal, whereas most L-ISA systems will have five scene arrays and two extensions as frontal. This higher spatial resolution allows for much enhanced localization accuracy and intelligibility in large audiences.

Fig. 2 – Audio-visual perception of classic stereo live sound system

Fig. 2 shows the limitations with stereo live sound. All of the sound sources/objects come from one place, in between the left and right arrays, making it difficult for the brain to separate the sound sources into individual objects/musicians. Another problem is that stereo live sound systems make the sound source appear to come from the loudspeaker array closest to the listener, creating conflicting audio-visual cues, causing confusion and fatigue for a listener’s brain (known as cognitive dissonance), as shown in Fig. 3. Stereo systems create inconsistent frequency response across the venue listening area due to interference between the arrays, known as comb filtering (more on this in my article in the March 2019 issue).

Fig. 3 – Audio-visual perception of classic stereo live sound system

Immersive systems have multiple main arrays providing for multiple single sources of discrete arrays/channels across the stage, providing a consistent frequency response and sound image for each of the sound sources. With a greater number of full-range loudspeakers in an immersive system, better spatial separation of the sound sources can be achieved, making it easier for the listeners to distinguish between the multiple spaced sound sources/musicians, as shown in Fig. 4.

Fig. 4 – Audio-visual perception of L-ISA live immersive system

I had a harder time imagining this sonic benefit, but demos have proven that this immersive system benefit is quite obvious! Immersive systems also allow much more accurately positioned sound sources — regardless of the listeners position in the main listing area — providing alignment of what you see to what you hear — for effortless association of audio and visual information (reducing cognitive load on the listeners), as shown in Fig. 5.

Fig. 5- Audio-Visual perception of L-ISA live immersive system

In Fig. 6, notice how the music production studio is represented as the small circle in the middle of the large amphitheater. Immersive system software now allows production professionals to create multi-channel surround sound imaging in the studio, and then scale it up to performing arts centers and large amphitheater venues as needed; the immersive software algorithm accounts for the increased delay time needed for a wide variety of venue sizes. Much like Dolby Atmos in commercial cinemas, immersive live sound systems can provide imaging from overhead loudspeakers and several surround speakers as desired; but again, note that the side-surround speakers may need to be compact line arrays, to project across large venue applications (see Fig. 1 and 6). Actual immersive (multi-channel) sound coverage of a very-large venue does have some limitations, as shown on December 2019 issue. So, for very wide/large venues, mono side-fill arrays may be needed for the extreme side/rear seating areas.

Fig. 6 – Fig. 6: Scaling up immersive sound from studio to large amphitheater

‡‡         Coming Up

Another challenge is that most immersive live sound systems have used five to seven large line-array hangs — these tend to occlude upstage design/graphics. With that in mind, I have begun work on adapting a high-performance one-box array I designed for a recent client (shown in the Aug. 2019 issue of FRONT of HOUSE), for use in low-profile multi-channel immersive loudspeaker arrays, to solve the visual conflict. Ideally, I will be able to team up with a reputable pro-loudspeaker manufacturer to bring just such an innovative immersive array design to market. See you next month!

David K. Kennedy operates David Kennedy Associates, consulting on architectural acoustics and live-sound system design, along with contract applications engineering and market research for speaker manufacturers. He has designed hundreds of sound systems for churches, schools, performing arts centers and AV contractors. Visit him at immersive-pa.com.

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