Introducing the 10.2 Surround Format
Actually it isn't quite so new considering Tom has shown this 10.2 technology for years and has10 such permanent facilities that he's built for others worldwide including -one at Bjorn's Audio Video in San Antonio . The practicality of this format is somewhat limited due to logistics of integrating the additional speakers for its realization and the fact that it does require significantly more processing power. The motivation behind 10.2 was to demonstrate that the audio industry focus on higher sampling rates is not going to produce the most perceivable difference. Since the limits of human perception have already been met in word length and sampling rate, the next revolution will inevitably be in the number of audio channels to better match human spatial sound perception.
In evaluating the important improvements which could be made to standard 5.1 in order to improve the surround sound experience, the first place to fill in is to the sides. Psychoacoustics research says that side reflections are important in the perception of source width and the preferred direction for such reflections is at 55 degrees. In response to this research, 10.2 adds new width Left Wide and Right Wide speakers and channels (with a 35 ms delay to simulate the first reflection of a typical shoebox shaped concert hall). These additional tracks are added in the mixing engineering phase.
A single discrete Surround Back speaker is utilized in 10.2 to fill in the wide gap left there by the standard surround speakers at ±110 degrees. The next thing to be reproduced was the ceiling reflection above the orchestra in concert halls. A Left Height and Right Height channel were subsequently added to more accurately recreate "depth" in the soundstage.
Finally, two independent subwoofer channels are provided, each bass managed from its respective side and also available for separate left and right LFE tracks. On most tracks this will still result in a dual mono subwoofer system, but the potential for greater fidelity is there with independent Left & Right subwoofer channels. Audyssey is still conducting research into the science behind this decision. They believe that although bass waves below 80 Hz are omnidirectional, there is research evidence that shows stereo bass can improve the sense of envelopment and add a further sense of realism to the surround experience.
10.2 Speaker Layout Diagram and Explanation
The above diagram illustrates the placement of the additional speakers along with the standard 5.1 ITU setup. The channel naming is as follows:
L, R, C, LS, RS, LHeight (LH), RHeight (RH), LWide (LW), RWide (RW), Back Surround (BS), L SUB, R SUB
To the standard 5.1 layout, 10.2 adds speakers based on both acoustical and psychoacoustical considerations. Side wall reflections in concert halls, for example, have been found to add to the sense of spaciousness when implemented properly. Ando found through extensive listening tests (Y. Ando, "Concert Hall Acoustics", Springer, Berlin, 1985) that there is a preferred direction for first reflections, preferred spectrum, and preferred delay. The LW and RW speakers are intended to reproduce such reflections picked up by wide or outrigger microphones in 10.2 recordings. A second, and equally important, role for the wide speakers is that they shorten the gap between front and surround speakers. This allows more accurate placement and panning of sounds from front to back.
The second most important reflection in a concert hall, after the side, is the one from the proscenium above the stage. The Left and Right Height channels are designed to reproduce the sound from that direction. They are also appropriately processed and delayed to seamlessly blend with the direct sound from L, C, and R.
Finally, the back surround speaker is used to fill in the gap between the left and right surrounds to allow for both discrete placement and seamless surround ambience.
The Need for 10.2 over Conventional 5.1, Based on Human Perception of Sound
5.1 channels (a term coined by Tom Holman at a standards meeting in the early 1990s) was the minimum number of channels needed to reproduce a front soundstage and an ambient surround impression. It is, by no means, the limit as human perception can discern many more directions. 10.2 was designed to fill in some of the perceptual gaps that are left unfulfilled by 5.1. For example, Makous and Middlebrooks (J.C. Makous and J.C. Middlebrooks, "Two Dimensional Sound Localization by Human Listeners," J. Acoustical Soc. of America, vol. 87, no. 5, May 1990, pp. 2188-2200.) showed that human localization is much more precise in the horizontal plane and the front hemisphere and degrades for the sides and rear. That would indicate that for a fixed number of channels, more should be allocated to the front than the back. Unfortunately, the surround industry has moved in the opposite direction by adding more surround channels than front channels (e.g., in 7.1 systems). While additional surround channels can be useful in reproducing ambient sound and improve audience coverage in large rooms, current systems do not map well with the needs of human perception.
In other work by Rebscher and Theile (R. Rebscher and G. Theile, "Enlarging the Listening Area by Increasing the Number of Loudspeakers," 88th AES Convention, 1990, Preprint No. 2932.) it was shown that there is a direct relationship between the size of the useful listening area and the number of screen (front) loudspeakers. Moving from 2 to 3 and then to 5 front speakers (as found in 10.2) the area in which imaging distortion is minimized increases from a few centimeters to over 3 meters.
From R&D to Production
We sat with Sunil Bharitkar and discussed the procedure for bringing new products to market. Sunil earned his PhD in the area of room equalization. When their research was in the formative stages and finally came to fruition, Chris, Tom, Phil, and Sunil decided to start the company and license the technology. They found that their objective and subjective measurement showed that MultEQ technology was solving many of the room correction problems that parametric EQ methods had been unable to solve in the past.
Research and development is the beginning of every new concept which is worked through and then eventually productized. Sunil interacts with both Chris & Tom (and also works closely with Philip Hilmes) to develop ideas into working models that can be expanded upon. These ideas are worked into a more refined product which then led to demonstrations to other companies. One of the primary tools he uses to do research is MatLab which is integral during initial testing phases. These working models then get passed on to the DSP engineering group - where they can port a real product to the appropriate DSP platforms. Having an efficient and well thought-out chain of events is core to what Audyssey does. They shared some of this with us and it breaks down as follows:
1) Identify the Problem
Chris Kyriakakis & Tom Holman identify the problem and come up with ideas to tackle it. For example, MultEQ was created because Tom was going into theaters with stacks of equipment and taking weeks at a time to complete what was a very laborious process to calibrate a large listening room. Lots of skills were needed and the process was laborious and could not be easily replicated in different rooms. Tom believed there had to be a way to develop an automated way to handle acoustical issues since the procedures and process were essentially repeatable and defined.
2) Research Phase
This is where Sunil Bharitkar gets involved and discovers how specifically Audyssey can fix the problem. For the original MultEQ, he was able to take USC research students and devote quite a bit of manpower to the task, using the tools and software that Audyssey makes available for tackling these issues.
3) Commercialize the Product
Phil Hilmes takes the ball from here, his job primarily being to lead the team of DSP engineers and make the solution practical. This means fitting it onto a DSP chip, making sure it operates in real-time, improving system efficiency, and verifying that the solution still meets the requirements of the product or software algorithm.
The final stage is where all of this R & D is recouped - namely licensing the finished product to consumer electronics companies. In the case of new hardware products, they bring them to market through the proper dealer network channels. Audyssey's goal is to work with all industries and markets: professional, consumer, automotive, and even the personal computing industry. They want to be anywhere speakers produce sound.
Audyssey offers 5 levels of licensing of their EQ technology as follows:
MultEQ Pro - Currently runs on the Audyssey Sound Equalizer standalone processor with 16x resolution FIR filters, up to 32 room measurement positions and enhanced (up to 64x resolution) bass correction
MultEQ XT - 8x resolution FIR filters with up to 8 room measurement positions
MultEQ - 2x resolution FIR filters and up to 6 room measurement positions
Audyssey 2EQ - 1x resolution FIR filters and up to 2 room positions
Audyssey EQ - fixed system correction intended for HTIB systems and digital TVs to better linearize system response
Audyssey algorithms are currently supported by Analog Devices and Texas Instruments chipsets allowing for a wider diversity of hardware platforms manufacturers can develop their receivers or processors on. Audyssey is currently working on integrating their technologies into car audio applications and home audio subwoofer systems.
Audyssey has recently introduced a new stand alone processor featuring MultEQ technologies but with double the filter resolution of what is currently available in receivers, as well as enhanced processing for bass correction. It is an 8 channel device that connects between the A/V processor and the power amplifier and is intended for systems with separate components.
Audyssey MultEQ Pro allows up to 32 calibration points (unlike the capped 8 position calibration of MultEQ XT). The Sound Equalizer is intended for the custom installer market. An Audyssey-trained installer uses the Installer Kit that comes with an individually calibrated mic (with cal file that matching it to an industry-standard ¼" B & K reference mic), calibrated preamp, USB cable, mic stand, and 72' of XLR cables. Best of all it comes in a beautiful padded carry case that can be taken on-site for MultEQ Pro installations.
Audyssey built a pseudo anechoic chamber where they measure each mic that ships with the MultEQ Pro kit. They take that response curve and compare it to a reference B & K microphone (model #4136). They measure the mic response and invert it to create a difference curve to correct the mic so it matches the response of the multi-thousand dollar reference system. The manufacturing variance between mics is great enough to warrant them to be serialized (this is then uploaded into the software). Not only is the mic calibrated, but the preamplifier is also measured so that its consistency is maintained throughout the entire signal chain. These measures are critical to achieve the precision needed for meaningful calibration across the entire frequency range.
The MultEQ Pro algorithms allow up to -20 dB cuts, and 9 dB boosts for the entire frequency spectrum it attempts to correct. It employs a -9 dB signal reduction at the input to maintain system headroom. It is designed for industry-standard pre-processor line-out levels of 1.5 Vrms.
While we sat in the Immersive Audio Lab, we were given a brief history of surround sound including Tom Holman's direct involvement with the birthing of these technologies. He was the first to call discrete surround sound a "5.1 system". As most home theater enthusiasts know, 5.1 stands for Left Front, Center, Right Front, Left Surround, Right Surround, Subwoofer (a limited bandwidth channel, hence the .1). The demo discussed our previously mentioned limitations of conventional 5.1 formats which included the lack of convincing front to back panning of information. According to research, human hearing has degraded localization capability at 90 degrees. The benefit of 10.2 allows for a more naturalistic surround presentation since it provides the critical height and width data our brains are most perceptually sensitive to.
At this point, our brains were nearly saturated with digesting all of this fascinating information and were finally ready to hear some demos. Audyssey conducted some demos in conventional 5.1 and in 10.2 to compare and contrast the experience.
First up was a Diana Krall demo. She was on stage with bassist backing her while she introed her band. The sound was expansive with the walls of the room virtually disappearing. There seemed to be no disconnect between hearing her in the Immersive Audio Lab vs actually being at the live performance. The only thing missing (and thankfully so) was the usually annoying viewer(s) behind us shouting or singing along off key while Diana was singing "All or Nothing at All".
The next track was a chorus and pipe organ piece by Tom Vigneri. The venue was Methuen Hall. In 10.2 you literally felt immersed into the hall. The recording was done with 24 individual mic scattered around the stage, with some located above the chorus and positioned at two different heights in proximity of the organ. Some of the mics were used to capture hall ambience as well as direct sound from the soloists. There was also a mic position facing the wall for capturing back channel information.
In 10.2 you really had that "live" experience. A quick switch over to conventional 5.1 collapsed the front soundstage, making the listening space seem much smaller and sonically dull. We no longer had the impression of the "live" experience which our ears quickly adapted to upon instantly hearing. The leap in sound quality between 5.1 to 10.2 is comparative to first hearing a 2CH recording vs a dedicated 5.1 recording. Once you hear the latter, it's difficult to go back to the former.
What was truly impressive about this recording was its authentic rendering that we've simply never heard in any conventional 5.1 recording. Chris told us the success of this recording had largely to do with the fact that when you record and mix the tracks yourself, and know the composer, it really goes a long way in ensuring you've captured and produced an accurate multi channel rendering of the experience.
Last but not least, we heard the beautifully recorded Herbie Hancock Butterfly song which we learned consisted of 48 original tracks that they remixed especially for this project.
In 10.2, the mix had a very pinpointing and enveloping soundstage which was undoubtedly thanks to the height and width channels. A good portion of this experience was lost once we switched to conventional 5.1. The recording now took on a dryer more sterile feeling.
Our visit to Audyssey and the USC Immersive Audio Lab was enlightening and refreshing. We were pleased to see the direction that this once little start-up company is now taking. They have broadened their horizons, achieving a much larger portion of the market share from entry level all the way to targeted custom installer solutions for uncompromised theater installations. Audyssey's future looks bright thanks to their very talented research and design staff, and savvy business folks who address market needs based on consumer feedback, professional feedback from installers and reviewers, and observed market trends. We look forward to exploring the Audyssey potential as it unfolds over the next few years into great new products and envelop pushing technologies.
Pictured left to right
(Clint DeBoer, Michael Solomon, Gene DellaSala, and Chris Kyriakakis )
For more information on Audyssey Laboratories, please visit www.audyssey.com .
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