Center Back Surround
Dear Gary: Salutations! First off, though this is extremely late in coming, I’d like to tell you what a thrill it was for my son and I to have met you at HiFi ‘97 in San Francisco. (We were one of the folks you videotaped at your booth that year.) Further, I want to congratulate Widescreen Review on its fantastic website (www. WidescreenReview.com). I’ve had it bookmarked on my browser ever since it was up and running, and it seems to just get better and better. Bravo! My purpose for writing you today (a rarity in my busy schedule, I’m afraid) is to solicit your assistance in solving a small home theatre puzzle. Allow me to preface my question with the December 8, 1998, announcement from Dolby Laboratories which states that Canada’s Famous Players exhibitor chain will be installing the new Dolby SA10 Surround EX adapters on 700 of its screens in time for the Memorial Day release of Star Wars: The Phantom Menace. Developed in cooperation with Lucasfilm/ THX, it is my understanding that this adapter added to the current Dolby Digital decoders in place at theatres will provide a dedicated center surround channel, enabling more realistic rear-channel pans, fly-bys, and fly-overs. (It’s true what they say—technology never stands still!) While salivating over this development, I can only hope that Surround EX will arrive stateside as well (read: Mann’s Chinese or Mann’s Village Westwood, the two most-likely 70mm houses in Los Angeles to screen Phantom Menace). In the meantime, I’ve been trying to figure out how I can create a similar effect with my own home theatre, and that is where you come into play, Gary. The one thing I feel is missing in my set-up (an all-digital, separates-based system centered around the Denon AVD-2000 Dolby Digital decoder and Millennium 2.4.6 DTS decoder fed into the AVD-2000’s 6-channel external input) is a rear center-fill effect. Then, it dawned on me that one of the earlier issues of Widescreen Review addressed this very topic. You went into wonderfully thorough detail, outlining the setup of your Reference System L, complete with photographs of both the layout and calibrating/set-up technicians at work. (At that time, I believe the magazine had recently upgraded from the Fosgate-Audionics Model 3A to the Citation 7.0 Six Axis system.) What I am interested in doing is summing the rear channel effect somehow to include a distinct, though maybe not exactly discrete, rear-center ambiance similar to the set-up in “L.” (I have an extra channel of amplification on my Parasound HCA-806 ready and available for this very function.) The problem is, I don’t believe the article addressed the name of the summing circuit’s manufacturer/model number used in conjunction with your Mirage 3-channel crossover. I am certain many of us readers of Widescreen Review are equipped to handle such a function without having to make the rather costly sacrifice of upgrading to a Citation processor. (Am I correct in assuming that the Citation Dolby Digital decoder add-on has such summing for its Six-Axis function built-in?). Any information you can provide will be of great help. And, if you no longer utilize a summing circuit, perhaps you can recommend a consumer manufacturer of such circuits to me and your readers. I think Surround EX will elevate the standard of the movie-going experience that much higher next summer. And, until such technology arrives on the consumer front (at least at an affordable level), concessions such as Six-Axis or summing circuits are more than welcome to make the home theatre experience “the best it can be.” Your publication, along with its thorough and informative software reviews, is a mainstay in my household, and I encourage you and your obviously dedicated staff to continue the great work. Looking forward to hearing from you.
Jon C. Worthey, Los Angeles, California
Editor Gary Reber Comments:
Just the other day I wrote an article for “Today’s News” for our webzine (www.WidescreenReview.com) about the new Dolby Digital Surround EX process to create a 6.1-channel theatrical surround format. Curiously, as I stated in that editorial, the format was inspired by Gary Rydstrom, Lucasfilm’s Academy Award®-winning sound designer and Director of Creative Operations for Skywalker Sound (Lucas Digital Ltd.) “I wanted audiences to be completely encircled by surround, as well as hear sounds played directly behind them.” Rydstrom says. “I wanted to develop a format that would open up new possibilities and place sounds exactly where you would hear them in the real world.” That, as our long time readers know, is exactly our philosophy which we have termed “holosonic™” soundfield creation. For years now, we have reproduced a phantom center back channel derived from the left surround and right surround discrete channels in a 5.1 mix or from the 5.0 Fosgate/Citation Six-Axis™ or Lexicon Logic 7 matrix systems that produce independent de-correlated surrounds. One method used is the two “discrete” surrounds are fed to a joining box with level control then to a dedicated power amplifier (mono block or the sixth channel of a multichannel amplifier). This is not the preferred method, however. The preferred method is to use a Dolby Surround/ProLogic or Matrix processor ahead the level control. We typically use this feature for our own gratification but do not review soundtracks off DVDs and Laser Discs using this enhanced soundfield method as no manufacturer to our knowledge provides for such a feature on their processor/controller. Ideally, this would be a discrete channel, though a matrix encoded back center channel would do a credible job as well (just as matrix PCM Dolby Surround ProLogic does a credible job at producing a “discrete” sounding centre channel). While this method when applied to a theatrical setting cannot be optimized for the entire audience, the end result can be quite effective and exciting. With Dolby Digital Surround EX, center surround information is reproduced by the speakers at the rear of the theatre (typically two to four depending on the size of the auditorium), while left and right surround information is reproduced by the speaker arrays at the sides. In a home theatre setting, where full-range matched loudspeakers can be positioned at equal distance from the primary listener’s “two ears,” (sweet spot) the resulting holosonic soundfield envelopment can be quite realistic. That is, assuming that the sound design optimally supports such and the mix is monitored and created on a matched near-field system to emulate a home theatre. This is why there should be an optimized speaker placement standard supported by manufacturers wanting to create the best home theatre experience possible. The Surround EX format is fully compatible with all existing 5.1 digital systems, including DTS Digital Sound and DTS Digital Surround (the home version) and SDDS. It requires the addition of a Dolby SA-10 surround adapter and wiring the speakers into left, right and center groups with the addition of a channel of amplification for the center group of speakers. With this new method the sound designer can create true “fly-over” and “fly-around” effects and side wall phantom imaging that sound smoother and are much more accurately placed, either directly behind or directly beside the audience. The Dolby Digital Surround EX format makes its debut with the May 21, 1999 release of George Lucas’ new Star Wars: Episode 1—The Phantom Menace. Another upcoming film soundtrack to be mixed in the new format, is DreamWorks’ The Haunting Of Hill House. We do not know the specifics of the electronic circuit design presume it is a “ProLogic”-like circuit. Look to Widescreen Review for an upcoming article describing the technical features of Dolby Digital Surround EX. As well, we are pursuing integrating the Dolby SA-10 adapter into a reference system. For years now I have urged several manufacturers to incorporate into their digital processor/controllers center back effect processing with level control. Issue 15 described the original unit I used, which was designed and hand-built by Ian Paisley, the designer of the Mirage® line of loudspeakers used in our Reference System L, and Director of Engineering at Audio Products International (API), the manufacturer of the Mirage and Energy lines. I had suggested to Ian that the circuit be incorporated into the Mirage LFX-3 electronic crossover as an extension of the breakthrough patented “phantom/real” image system incorporated therein, whose genesis is an idea I presented to Ian in 1993 (see Issue 16). This exclusive LFX-3 circuit allows you to dial in the perfect blend between real full-center channel sound (matrix derived or discrete) and the phantom image created by left and right speakers alone. I have praised this circuit repeatedly in previous editorials and responses to readers letters. Simple, but effective, it generates a hybrid center channel acoustic image. In the phantom position the center channel is turned off. Conversely in the real position there is only the hard real center signal. You can generate an image that is a combination of x percent real center and y percent of phantom center. And by doing that you can eliminate the “in your face image” that the real center channel often gives you and the accompanying loss of the spatial characteristics of your left and right speakers when the center image comes from the actual center channel speaker. It allows you to simultaneously retain the desired spatial aspects conveyed by the left and right speakers and lock the image to the screen center with x percent of the real center signal. My typical usage is in the region of 60-50 percent real center and 40-50 percent phantom. But when I am reviewing soundtracks I defeat the circuit and listen only in the real center mode. Uniquely, the Mirage phantom/real system can create the most balanced, natural soundstage perspective imaginable when used with a well designed speaker to reproduce center sound. Now, once a hard center back surround channel is created by this other matrix method of summing the left surround and the right in-phase surround, that signal can be processed along with the two surround signals through a LFX-3 and controlled in the same manner as with a LFX-3 used for the main front three speakers. The result is enhanced dimensional depth in the rear hemisphere of the soundfield. Perhaps now that Dolby and Lucasfilm have announced their co-developed Surround EX format, Ian Paisley and others will seriously consider implementing the functions I described for creating a center back surround channel from summing the two independent surround channels. I had hoped that the new Citation 5.0 AV Controller would incorporate a center surround processed output using Six-Axis technology. Other choices that work well are to use the Fosgate Model Five or Model 3A, or a Citation 7.0 and a 5.0, if you wanted to spend the money. But in terms of cost effectiveness the Fosgate Model Five is a favorite choice of mine and it has the simplest signal path and sounds very clean. In the Fosgate and Citation processors, use either Dolby Pro Logic or Six-Axis. Uniquely, the Dolby Digital Surround EX format will use matrix encoding so as to create a back center channel encoded at the time the left surround and right surround channels are produced and mixed on the dubbing stage. Should that be the case, then Dolby is rumored to be preparing to license an official consumer version of the SA-10 in conjunction with Lucasfilm as part of the THX Ultra products licensing program. At this point, I don’t have the specifics.
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