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Dancing Around Surround

Surround sound is where the action is: both on the TV screen and behind the scenes. Cable and broadcast networks increasingly are delivering an audio experience that places viewers in the crowd at the Super Bowl or on the battlefield of the latest Hollywood blockbuster.

For all its effectiveness, though, surround sound is still an emerging technology. At the station level, the need for surround sound on the evening newscast or local cooking program is negligible. It will be the network feeds that push audio mixing and delivery in new ways.

"We continue to hear that the networks want the Dolby Digital light on stereo receivers to light up, and that only happens when they're receiving a 5.1 surround sound program," says Tom Daily, professional audio marketing director for Dolby. "There will be more 5.1 programming on the networks this fall, and, as cable networks start going to HD, they'll want to launch with 5.1 capability as well."

For console manufacturers like Solid State Logic (SSL), the move to HDTV and DTV channels is giving renewed energy to the market. Says Vice President, Broadcast Sales Steve Zaretsky, "Audio is certainly becoming a bigger priority."

SSL's top console for the broadcast market is the C100. It has up to 128 input channels, but, says Zaretsky, channel capacity isn't what's most important to broadcasters. For them, it's the ability to tie into as many tape decks, video servers, cameras and other devices as possible. "Because of that need, the C100 has a digital router so it can take sources and send them to different places without mixing them," he says. "It can route to as much stuff as it's plugged into."

Another feature local broadcasters are looking for is a console that has an easy migration from mono to stereo and, eventually, to 5.1 surround sound. Today, lots of broadcasters still send out only a mono signal. That will change soon, though, making future-proofing of audio gear a must. SSL, for example, has incorporated a touchscreen that allows users to quickly switch among the meters for mono, stereo or 5.1 signals. "It's very simple and visual," says Zaretsky, "and users won't need to remember cryptic programming code."

As much as new consoles may be in a station's future, the real need will be for the gear to relay 5.1 surround sound signals from the network to viewers. One method is to use Dolby E, the sound-equipment maker's digital distribution system that delivers Dolby Digital signals. It allows networks to send (and stations to receive) up to eight channels of audio plus attached metadata that ensures that the right signal is sent to the right device. Most important, it ensures that audio and video frames are in sync.

CBS stations have been adding Dolby E decoders, but the other networks are slow to join them. Both Fox and PBS have their own systems, in which the audio is embedded at the network and sent to the stations as part of a transport stream. The station passes the stream directly to the viewers.

One challenge Dolby E will face in the future is the need to serve the Spanish-speaking audience with more than just a mono audio track. As the Hispanic market grows in size, so will the pressure to deliver a high-quality audio experience. But there might not be enough bandwidth to do that, given the current delivery mechanisms. For example, adding another eight channels of audio requires an additional 2 megabits per second (Mbps) of bandwidth. That extra demand could impact video quality.

Looking to the future, Dolby unveiled its Dolby Digital Plus in April. It provides Dolby 5.1 surround sound to next-generation video systems like MPEG-4 (Part 10) and Windows Media 9. The Advanced Television Systems Committee (ATSC) should approve it within a few months.

"This allows broadcasters and others to deliver audio with similar quality to Dolby Digital with about 30%-40% bandwidth savings," says Daily.

Tim Carroll, ATSC chairman of audio issues for the standards-evaluation working group, says that a regular Dolby Digital signal needs to be sent alongside the Dolby Digital Plus signal. That means "Dolby Digital Plus has to go through a transcoding step so that it's backwards-compatible with Dolby Digital [receivers]," he says. For example, the set-top box that would be used to receive the MPEG-4 video stream receives the Dolby Digital Plus signal and then converts it to Dolby Digital before sending it to the stereo receiver.

Daily says, when content distributors move to advanced video compression—such as MPEG-4—broadcasters will be aggressive with compression, making Dolby Digital Plus attractive. "Computer chips have gotten faster so we can do things that were unthinkable 10 years ago," he says. That goes double for television operations, especially when it comes to audio.