There is extreme “channel confusion” taking place in the custom installation industry, but it has nothing to do with Internet reselling or distribution. It’s the channel confusion related to “discrete” versus “processing” channels in surround-sound or new immersive audio setups.
Integrators are proactively deploying object-based surround sound systems such as Dolby Atmos, DTS:X and Auro without surround sound processors (SSPs) or receivers (AVRs) that can accommodate more than 11 discrete channels. The result is clients are possibly not getting what they paid for in their home theater immersive audio system.
Arnaud Laborie, founder, CEO and chairman of the board for Trinnov Audio, makers of SSPs, notes that the problem is that integrators are confused between a “discrete” channel and a “processing” channel.
Laborie deciphers the situation for CE Pro:
“Dolby Atmos and DTS:X are both object-oriented formats, and Auro has announced that it is moving in this direction as well. ’Object-oriented' in this context means that once you go beyond the basic 7.1 speaker setup that we all know well, additional sounds are not assigned to specific ‘channels.’
“Instead, ‘audio objects’ are defined composed of a combination of the sound itself and metadata to describe the location of the sound over time relative to the main listening position (MLP). It is the responsibility of the SSP or AVR to ‘render’ these objects appropriately to the available speakers.
“Almost all current SSPs employ a DSP platform from one of a couple DSP chip companies to do their 3D Audio decoding and rendering of the audio objects. These companies depend on large volumes in order to recoup the significant investment in R&D and tooling required for designing new chips. This need for high volume leads to them making decisions about their architectures that are driven by the mass market.
“Currently, we have not been able to verify any DSP-based solutions for more than 11 uniquely-rendered main channels (excluding subs). As recently as ISE, a couple companies announced the ability to move this number up to 13 from 11, which is certainly a step in the right direction. This means that, regardless of the number of speakers used, the effective spatial resolution is 7.1.4, or perhaps 7.1.6, regardless of how many output connectors reside on the rear panel.
“For example, a large theater might have several speakers on the left sidewall; however, they would all be receiving the Left Surround (Ls) signal, albeit perhaps with different delay and level adjustments.
“We expect that a DSP-based solution for perhaps as many as 16 discretely-rendered channels will become available toward the end of 2017, which will be an improvement, to be sure. However, even then, manufacturers will have to develop (or update) their products using the newly-introduced DSP engines, which will take some time.
Conflicting Immersive Audio Format Specs
“There remain differences based on the architectural decisions made by the three immersive audio companies. For example: The Dolby Atmos specification allows for a maximum of 34 unique speaker locations (plus LFE), and provides for up to 24 separate speakers with unique signals at listener level, plus another 10 channels above the listener.
“Auro 3D provides for as many as 13 unique speaker locations (plus LFE). Hence, if you have a high-channel-count system, you will usually end up arraying some of the channels by sending them to more than a single speaker location.
Related: Home Theater Demo Guide for Showing Differences Between Immersive Audio Formats
“DTS:X currently allows for 11 speakers out of a total of 30 possible locations (plus LFE), or a 7.1.4 arrangement in the commonly-used parlance. Once again, in a higher-channel-count system, you would normally end up setting up arrays of surround and height speakers to ensure that all the speakers are used.
“Clearly, Dolby Atmos currently provides the greatest potential for high spatial resolution. Trinnov recently announced a coming, optional software update that will allow it to render all 34 discrete channels provided for in the Dolby Atmos specification, plus another 14 output channels (48 total) to support complex bass management systems, or for speakers employing the Trinnov's Altitude32’s active crossovers.
“However, the differences do not stop there. All three immersive audio formats listed above have different recommended locations for the additional loudspeakers (beyond the basic 7.1 layout we have used for years). This fact has led to some people advocating for multiple sets of somewhat redundant loudspeakers, and using only the ones that are pertinent to the format being played at the moment.
“We feel this is a significantly inefficient waste of available resources. Moreover, it seems that it must be a difficult proposal for the client to accept: paying for perhaps 30 channels of amplification and speakers and then using only a dozen or so at any one time.
What Is the Solution?
All is not lost for integrators. Laborie explains that Trinnov has a 3D Microphone that can accurately measure the actual location of each speaker in space (to within 2 degrees of azimuth and elevation, and 1cm in distance), relative to the reference position.
That information, combined with the company’s software called Remapping technology, can create phantom images of these sound objects that will be perceived as being located accurately, even if there is no speaker at the indicated location.
Laborie explains:
“In principle, this process acts like stereo imaging, except that it operates all around you rather than only in front of you. This combination of unique technologies allows us to reproduce all three immersive audio formats from a single, sensible array of loudspeakers.
“As with stereo, these phantom images work best when you are in the ‘sweet spot.’ When multiple listening positions are considered, the rationale for high speaker counts becomes even stronger. This is so because the location of the sound will be less dependent on phantom images and instead be determined more by the location of actual loudspeakers.
“This follows the same reasoning as having a Center channel speaker rather than relying on the phantom image from Left and Right. It locks the sound to a known, physical location, regardless of where you sit in the audience.
“However, adding additional speakers to create great spatial resolution only works if you can process all of these extra speakers’ signals individually, and with full knowledge of where they exist in the actual listening space.
“Imagine entering an old-fashioned hi-fi demo room with a wall full of left/right pairs of speakers. Now imagine that all of them were playing the same stereo signal, at the same time. You would not expect the imaging to be precise (or even good), regardless of where you were in the room. This situation is analogous to reproducing multichannel soundtracks on more speakers than there are discrete signals to be used. At best, you have an extremely blurred, unfocused sound image.
“There is no question that maximizing the immersive audio experience available is both complex, and also extraordinarily rewarding. There is no substitute for a truly high-resolution spatial audio experience to complement the latest offerings in high-resolution video. Optimizing the design and implementation of these systems requires experience and sound judgment as well as technical skills. The extra effort is worth it.”
