SPOTLIGHT ON THX SURROUND EX by Shane Buettner

THX recently shook up the consumer electronics world with their announcement at CEDIA Expo 99 that they would be exclusively licensing and offering a new consumer digital surround sound technology, THX Surround EX. What's more, the first DVD title encoded in Dolby Digital Surround EX, Austin Powers: the Spy Who Shagged Me, is barely more than a month away with more titles to follow. Upgrades for existing surround processors will be offered just before this title's release on November 16^th, and one would presume more hardware support, and perhaps even titles, will arrive for the Christmas rush.

Now, the thing that may be confusing to some is that THX Surround EX is the processing technology used to decode Dolby Digital Surround EX soundtracks. In other words, the software will be encoded in Dolby Digital Surround EX, which will be decoded using THX Surround EX processing. Dolby Digital Surround EX is Dolby's latest theatrical digital surround sound format known as which made its debut earlier this year with Star Wars Episode 1: The Phantom Menace. I thought it would be appropriate to give people a heads-up on what Dolby Digital Surround EX is, and how THX is bringing this technology to the home.

Dolby Digital Surround EX

Dolby Digital Surround EX was co-developed by Lucasfilm THX and Dolby Laboratories. Gary Rydstrom, Lucasfilm's award-winning sound designer and Director of Creative Operations at Skywalker Sound, drove the creation of this format to coincide with the mixing and theatrical release of Phantom Menace. Simply put, Dolby Digital Surround EX is a"6.1" channel format that adds a "rear" surround channel to the existing 5.1 channel Dolby Digital Surround format, allowing sound designers and mixers to "encircle the audience with 360 degree pans and allows more realistic fly-over and ambient sound effects." What this means in a theater setting is that the speakers along the side walls on the left and right sides will, respectively, be left surround and right surround, while the speakers along the back wall of the theater will comprise the rear surround channel. The addition of this rear surround channel obviously increases the filmmakers' ability to put sounds "behind" you as well as increasing their ability to pan sounds around you in a discrete, realistic manner.

The technology behind this is essentially the same matrix encoding-decoding technology used by Dolby Pro Logic to derive the front center channel from the front left and right channels. When the soundtrack is mixed it is a discrete 6.1 channel mix. The rear surround channel is then matrix encoded into the left surround and right surround channels of the 5.1 channel mix, resulting in a 5.1 channel printmaster that is 100% backward compatible with existing 5.1 channel decoders. But when played back through EX compatible equipment this rear channel is "dematrixed" out of the left and right surround channels and steered into the rear channel. The additional equipment required to employ Dolby Digital Surround EX theatrically is a Dolby SA 10 surround decoder which uses a Dolby Pro Logic decoder chip operating in the analog domain.

DTS also has a theatrical version of this technology called DTS ES which performs its rear channel matrix decoding with technology that is similar to the Dolby approach with the exception that it operates entirely in the digital domain with 24bit precision. DS ES is compatible with any existing EX encoded 5.1 printmaster as the rear surround channel information is matrixed into the surround channels prior to being encoded in either format.

In addition to Phantom Menace, the following films have been released theatrically in Dolby Digital Surround EX: Austin Powers: The Spy Who Shagged Me, and the Haunting. Upcoming releases scheduled include Toy Story 2, The Fight Club, and The End of Days.

THX Surround EX

Dolby Digital Surround EX has been licensed by Lucasfilm THX, the product's co-creator, and is coming to the home theater market as THX Surround EX, available exclusively in THX Ultra certified products. Where it gets interesting here is that THX Surround EX processors will be required to employ a 7.1 channel configuration, using two speakers to recreate the rear surround channel. In this configuration you will have the standard left, center, and right channels up front, with the left and right surround channels placed directly to the sides of the listening area, and two more speakers directly behind the listening area comprising the rear surround channel. Note that even though there are two speakers in the rear that the signal in these speakers will be playing back in mono, comprising one channel of sound, with no stereo separation of the signal (just as the surrounds in a Dolby Pro Logic or 2.0 Dolby Surround soundtrack are mono.)

Dolby Digital Surround EX is compatible with all existing DVD players and does not require deployment of new Dolby Digital chip sets to be used in new products or upgrades to existing processors. Essentially the way this works is that a DVD will have a Dolby Digital Surround EX 5.1 soundtrack with the rear surround channel information matrixed into the left and right surround channels. This DD-EX 5.1 soundtrack is 100% backward compatible with existing DD decoders (and their chip sets) For this reason THX is "trying hard not to call it a format," and refer to it instead as a new "feature of 5.1." DVDs encoded in Dolby Digital Surround EX will carry a digital flag within the "metadata" of the DVD that alerts a THX Surround EX decoder to the presence of a compatible soundtrack. The processor then decodes the soundtrack, and employs Dolby Pro Logic type matrix decoding on the left and right surround channels to derive the rear surround channel information and steer the signal to the rear surround channel speakers. This post processing of the signal is performed entirely in the digital domain, just any other type of DSP mode would be. An easier way to think about this is to think of it as an additional post-processing mode available for you to use with DD 5.1 channel material. Some processors allow you to use DSP modes that recreate the ambient environment of churches, or jazz clubs, or what have you, along with your 5.1 decoding. This is the same thing, essentially performing the extra matrix decoding of the surround channels on top of the decoding the DD 5.1 soundtrack.

To ensure a coherent soundfield, THX is also requiring that certified THX Surround EX processors be able to implement bass management, independent time delays, and level adjustments for each of the two speakers employed as the rear surround channel. THX Re EQ on both speakers comprising the rear surround channel is also required.

Another question raised by THX' licensing of this technology is whether releasing a DVD title encoded in Dolby Digital Surround EX would require that the title be mastered under the auspices of the THX Digital Mastering Program (THX DMP.) According to John Dahl, Certification and Operations Manager of THX Product Management and Testing, DVDs will "not necessarily have to be THX Digitally Mastered titles." In other words, a title can be Dolby Digital Surround EX encoded, but doesn't have to be a full-blown THX DMP title.

The THX EX Surround Layout (not to scale)

Not Quite the Only Game in Town

As noted above, THX Surround EX processing is exclusive to THX Ultra certified products. But there are at least two other companies offering products that do roughly the same thing. ADA has a "6.1 Surround" processor, and SMART Theatre Systems CS-EX-JR-1 both perform matrix encoding on the surround channels to extract a rear surround channel, and both can employ a 7.1 channel configuration to do so. Both perform this matrix decoding in the analog domain, but the similarities end there. While both devices will only work with processors/receivers that are already 5.1 capable, the SMART adapter will only work with processors/receivers that have line level outputs (analog with RCA connectors.) ADA, on the other hand, has another add-on device called a "Speaker to Line Converter" that will take speaker level outputs and convert them to line level for use with their 6.1 Surround adapter. This effectively means that their technology will work with any existing 5.1 channel setup. SMART claims their product is superior to the Dolby Pro Logic based approach to the matrix decoding by their competitors. Interestingly, both products are also made for use with non EX encoded material, i.e., existing 5.1 channel soundtracks.

THX, for their part, believes their licensed products will represent the only approach that results in "accurate presentation of film sound." Correct bass management, independent time delays, all of which will be performed in the digital domain in THX Surround EX licensed products, are considered necessary by THX to recreate exactly what was on the soundtrack in the dubbing stage (most of which are THX facilities.)

But the thing to note here is that, at least in theory, both the ADA and SMART devices should offer proper decoding of Dolby Digital Surround EX encoded material, albeit in the analog domain, at least so far as the actual matrix decoding is concerned. The digital flag in the metadata of a Dolby Digital Surround EX encoded DVD merely alerts a compatible processor to its presence and automatically engages the additional matrix decoding of the surround channels to extract the rear surround channel. With one of these third party adapters you would simply have to make sure to manually select EX playback mode when playing Dolby Digital Surround EX encoded material (or simply leave it engaged constantly to derive whatever benefit may be gained with non EX encoded material.)

Upcoming Hardware & Software Support

One of the first THX Ultra licensees out of the gate will be Lexicon, offering upgrades of their current DC-1. DC-2 and MC-1 processors around November 1st, as well as implementing THX Surround EX in future releases of those products (JBL Synthesis is also offering a processor, but their processors are made by Lexicon with JBL faceplates.) Onkyo's Integra Research RDC-7 processor and Mark Levinson's upcoming No40 Controller will both be THX Surround EX enabled. Pioneer Elite plans on incorporating THX Surround EX technology into its next generation of products. THX's John Dahl assured me that more manufacturer announcements would follow, even though he wouldn't comment on specific companies. It's probably a safe bet that any manufacturer that's a already THX Ultra licensee will be looking into this.

DTS has no plans at this time to market a consumer version of their DTS ES theatrical format, but the key thing to remember is that the information is already there. DVD soundtracks are most often made from 5.1 channel theatrical printmasters. 5.1 theatrical printmasters of EX encoded films already have the rear surround channel matrixed into the surround channels before Dolby or DTS encoding. That is what allows DTS ES cinema adapters to extract the rear surround channel from the existing surround channels of their soundtracks, and the same should be true in the consumer realm. The 5.1 printmasters that were used for theatrical prints (and will be used for the DVD soundtracks) already have this information on them, its just a matter of decoding it and matrixing out the rear surround channel.

Since THX Surround EX is cross licensed between Dolby and Lucasfilm THX it seems very unlikely that a THX Surround EX processor will recognize a DTS ES data flag. Beyond the digital flag issue, however, one should nevertheless be able to decode a DTS ES rear surround channel with one of the third party devices, if not with a THX Surround EX processor. However, THX Surround EX can be forced into the on position on the processor, meaning that it could be used with DTS ES DVDs or other non Dolby Digital Surround EX encoded material.

New Line Home Video's Austin Powers: The Spy Who Shagged Me will the first Dolby Digital Surround EX DVD release, although it will not be a THX DMP title. Any future New Line releases will be also be fair game. As Fearless Leader Peter Bracke reported on 9/29, Dolby Digital Surround EX DVDs from Fox and Universal are in the works, or "under discussion," while Columbia, MGM, and Warner have "no plans to release Dolby Digital Surround EX discs at this time." Paramount, Buena Vista, and Dreamworks had no comment or information available at this time. Dreamworks' DVD product is affiliated with Universal for distribution, which may or may not be meaningful to the upcoming release of The Haunting, which featured a Dolby Digital Surround EX mix theatrically. At CEDIA at least one manufacturer rep referred to the possibility of Dolby Digital Surround EX remasters of previously released titles, but we've received no confirmation on that from any of the studios at this time.

Final Thoughts

As a Lexicon MC-1 owner I will definitely be one of the first kids on the block to have THX Surround Ex in my system. But I must say that my initial experiences with the product have been somewhat underwhelming. Phantom Menace and Disney's Tarzan are the only theatrical releases I've seen (and heard) in Dolby Digital Surround EX, both of which I saw in THX approved theaters. In the case of Tarzan no conclusions could be drawn from the experience as the theater had problems that made any evaluation of the format impossible. Phantom Menace was terrific, although I have to say I seldom heard anything from the EX encoding that noticeably enhanced the experience. I didn't hear anything that sounded like it was directly "behind" me, but there were a few pans from the surround channels to the rear surround channel, and vice verse, that were impressive. They were smoother, and the interesting thing was that it seemed to enhance the directionality of the surrounds. But the improvements I heard were rather subtle and certainly are not as profound as going from matrixed 4 channel surround to discrete six track, as was the case a few years back with the advent of digital surround sound.

On the consumer side, my first impression is even weaker. At the Onkyo Integra Research booth, Peter Bracke and I attended a demo of Dolby Digital Surround EX that left a lot to be desired. I will say that this experience is probably not representative of the real potential of this format, which I believe has yet to be realized. The equipment used was the Onkyo Integra Research RDC 7 processor along with the RDA 7 multichannel amplifier. The first clip played was a bizarre audio only piece called "Jungle Sounds." Aside from the sounds of the jungle and the animals, halfway through there are people trouncing through the jungle and firing weapons and then a helicopter circling around. It was full of ping pong style sound effects that bounced from channel to channel as opposed to smoothly panning around the room. Nothing was coherent about this piece, especially the LFE channel. When the helicopter shows up, you hear the blades and then as it gets closer, the LFE kicks in and it was so loud and low that it seemed to have nothing to do with the rest of the sound effects related to the helicopter or its impending arrival. There seemed to be serious frequency gap between the speakers and the subwoofer. What followed was the trailer for the Astronaut's Wife and the "Tex" THX trailer, and I honestly didn't hear anything indicating I was listening to Dolby Digital Surround EX encoded material. In fairness, I think room set up and certainly calibration of the equipment involved was a major issue, especially the LFE channel level setting. I also think the learning curve is going to be a factor here as mixers learn to use this new tool. The "Jungle Sounds" piece was poorly produced and gimmicky as opposed to the kind of seamless 360 degree soundfield that EX encoding has the potential to offer. But I'm definitely looking forward to getting THX Surround EX upgrade in my listening room to hear it for myself with properly calibrated equipment and properly produced material before I make any real assessment of the format.

For more information on getting THX EX in your home, visit our three-part piece on home EX setups:The Path To THX EX, A Set-Up Procedural, and Pseudo-EX Setups. Also, for more on THX itself, visit The THX Factor overview, as well as the web sites of THX and Dolby Labs.

Special thanks to THX's John Dahl for his help in the writing of this article. Additional Source: "Dolby Digital Surround EX" by Perry Sun and Gary Reber, Widescreen Review, Issue 32.