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Surround Sound for HDTV

Mar 1, 1999 12:00 PM, Mel Lambert

Time and tide, as we all know, wait for no man. In the world of high-definition video, the broadcasting and post industry now has a number of creative production tools available that can dramatically improve the quality of images being relayed to the consumer audience. And audio is not trailing behind. In addition to familiar film-dubbing and delivery techniques, full 5.1-channel digital transmission capabilities are now available to broadcasters, courtesy of the emergent Advanced Television and DTV standards.

The first use of all-digital surround sound broadcasting occurred recently during the world-famous Tournament of Roses Parade, which is held each New Year's Day in Pasadena, California. For the event, Tribune Broadcasting's KTLA-5, the Los Angeles-based broadcaster responsible for local and nationally relayed coverage of the proceedings, contracted National Mobile Television's new West Coast-based HD-2 High Definition Mobile Truck to provide full-bandwidth HDTV 16:9 pictures and simultaneous NTSC 4:3 transmissions. The triple expandable NMT's HD-2 can come equipped with up to 16 Sony HDC-700HD studio cameras or up to 16 HDC-750 HD portables.

While Channel 5 carried conventional NTSC-format pictures, KTLA-TV's Channel 31 broadcast a simultaneous high-def 1080i signal in 16:9 with companion 5.1-channel digital sound. KTLA also unlinked HDTV signals to Direct TV for display via satellite on rented 16:9 receivers. (The first shake-down session for HD-2 occurred in late-November during CBS Sports' coverage of an Oakland Raiders football game. NMT's companion HD-1 truck is based on the East Coast and operates out of New York.)

In rear of the 53-foot HD-2 truck, industry veteran Ron Estes manned an all-digital Sony OXF-R3 "Oxford" Mixing Console to prepare a variety of stereo and surround sound mixes. The OXF-R3 is equipped with 48 assignable input faders that are capable of accepting sources from 104 mic/line-level inputs. A total of 48 multi-track bus outputs are available, together with fully resettable EQ and dynamics processing. The LCRS Surround Sound monitoring system comprises an array of three Genelec monitors in front-mounted just above the console on the front wall-and a pair mounted on either side of the mixer's position. An outboard Yamaha all-digital 03D console was also available for additional sources, but Estes did not use it during the Tournament of Roses broadcast. Estes has many years of experience with surround sound mixing, dating from his days on The Tonight Show with Johnny Carson; he has also handled broadcast sound for the Tournament of Roses Parade for the past six years.

"My brief was to focus on the 5.1-channel discrete surround sound mixes that would accompany the HDTV broadcasts and, at the same time, monitor the down-converted, matrix-encoded stereo audio being broadcast with conventional NTSC-format pictures," recalls Estes.

He folded down his discrete, five-channel mix into a four-channel feed for a Dolby Surround encoder by simply summing left-surround and right-surround and slitting the center channel equally to the left and right channels.

Using the output from a collection of crossed coincident-pair and stereo microphones rigged on tall stands along the Parade route, Estes was able to follow the progress of the colorful floats as they made their way through downtown Pasadena. "From the viewer's point of view," he explains, "the Parade was passing from left to right across their screens, so I elected to maintain a consistent perspective of being down at the front of the crowd surrounded by the sounds of the parade." Having routed the various microphone sources to separate channels on the Sony OXF-R3 "Oxford" from left to right, he was able to simply raise and lower discrete faders to favor specific sections of the Parade as it passed in front of the high-def cameras laid out along the route. Announcer microphones were routed via the console into the center channel.

"Starting from the left-front and right-front stereo sources, I panned some of the front signal into the rear surround channels and used a couple of digital reverberation systems [including a Lexicon PCM-91 system] to create some ambience," says Estes. He also used additional microphone sources to develop a general ambience "wash" that was fed at a lower level to the surround channels.

"We also decided," Estes recalls, "to drop the low-frequency ["0.1," or bass-extension channel] because there was sufficient energy in the front and surround channels." Elimination of a dedicated LFE channel also frees up additional signal bandwidth for the Dolby AC-3-encoded audio channels that accompany a 1080i HDTV signal and is said to improve the overall fidelity of the remaining left, center, right, and surround sound channels.

"My overall scheme, if you will, was to create a surround sound mix that placed the [viewing] audience in the center of the crowd with a forward dominance to reinforce what they were watching on the screen."

Estes maintains that a dedicated, five-channel mix is far more realistic for home audiences than a Dolby Surround mix, which the conventional left and right stereo to TV broadcast bandwidth provides. "There are always compromises," he stresses, "when using [matrix-encoded] surround created from a four-channel balance and transmitted as a two-channel left to right signal. Because of several technical factors, signals need be panned to fixed positions to survive the 4:2:4 encoding process; specifically, stereo sources, if not blended carefully, can end up being summed and mixed into the phantom-center channel. But, because we have a discrete left-center-right mix that is sent directly to [a digital-capable receiver], broadcasters can maintain a higher degree of signal integrity throughout the transmission path. In practical terms, what I am hearing in the truck at the digital console is exactly what the home audience will be able to enjoy [via Advanced Television transmissions]."

The Sony "Oxford," Estes confides was reasonably easy to master, and simple to use. "Because everything was being broadcast live, I did not use any automation. The assignable EQ was very useful because I could develop a standard equalization profile for a critical pair of microphones and then 'copy' and 'paste' those settings to other channels. I used a standard filter of gentle low-frequency roll-off-to reduce 'boomyness' and rumble-plus a tough of high-frequency boost to brighten the sources. It saved a lot of time!"

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