Surrounded by Options

Broadcasters face choice of using a discrete or matrix-based audio system

It's obvious why the pretty pictures of HDTV (and DVD, for that matter) get all the attention on the trade-show floors and consumer-electronics displays. For many broadcasters and viewers, though, there's growing awareness that sound is just as important.

CBS and the Grammys stepped up with an impressive display of 5.1 surround sound for the 2003 Grammy Awards coverage, and ABC's Sunday Night Movies
has a wow factor as well. And, this week, Fox Sports will do a 5.1 broadcast of the Major League Baseball All-Star Game.

The reason for the interest on the part of broadcasters is simple: Surround sound has taken off at the consumer level. The explosion of DVDs, which have soundtracks mixed for 5.1 Dolby Surround and DTS Surround, is one factor. The other is the advent of cheaper speaker systems. Packages start as low as $200 and often come bundled with new receivers, making it much easier for the average consumer to experience surround sound.

For broadcasters and cable networks, there are two primary ways to offer surround sound. One way is a discrete 5.1 system, which sends six separate audio signals to five speakers and a subwoofer. Dolby Digital, which was tapped as the standard for DTV, has Dolby 5.1, its highest-quality system available for broadcasters.

More than 100 HDTV and SDTV broadcasters around the world currently use Dolby 5.1, according to Tom Daily, Dolby marketing director, professional audio.

Because Dolby 5.1 has discrete channels, it raises the technical challenge along with the quality level. For example, CBS's broadcast of the Grammys in 5.1 required HD encoders capable of carrying the signal as well as Dolby E decoders and Dolby encoders at stations. It also required audio delay gear because the Dolby system introduces about 7.5 frames of delay because of compression.

For broadcasters not up to the discrete challenge, there's another choice: the matrix route. Both Dolby and SRS Wowcast offer matrix-based systems, which send the six channels of audio over two audio channels.

Daily says Dolby Surround Pro Logic matrix four-channel surround-sound system can be carried to the home via any two analog or digital delivery systems.

"Matrix surround technologies use phase and amplitude relationships between the two channels to position the sound among the five speakers," he points out.

SRS Laboratories' Circle Surround technology is being used by ESPN and also by ABC, CBS, Fox, NBC and PBS, according to SRS Labs Director of Sales Mike Canavaro. The system includes the CSD-07 Circle Surround Decoder and the CSE-07 encoder.

SRS Wowcast Vice President of Engineering Alan Kraemer says that one advantage his company's system has over Dolby's is that it doesn't use compression. That means less delay (Circle Surround delay is less than one-third of a frame, he says) and fewer artifacts.

"The audio can go from a fairly low bit rate to a full PCM uncompressed rate," he says. "There are none of the artifacts that come with perceptual coding. You do need to know how to mix for a matrix system, although some of the steering we do helps out."

The system is can also handle 6.1 surround sound. When ESPN airs the Espy awards on July 16, it will be the first telecast in 6.1 surround sound.

"There's a sensing logic in the decoder that determines the degree of correlation between the surround channel," Kraemer says. "If that is fully correlated, then there is an output in the rear center channel. On the encoder side, we have an input that guarantees what you put into that input will be fully accommodated."

Dolby's Daily says matrix systems should never be viewed as a substitute for a discrete-based 5.1 system: "They will never offer the performance of a discrete system."

He does, however, see an either/or decision between matrix technologies. Dolby will begin shipping the Dolby Pro Logic II DP563 encoder later this month.

"We've found that broadcast customers prefer Dolby Pro Logic 2 because they know that Dolby pays particular attention to placing sounds in the assigned channels," Daily says. "Over the next few years, we expect to see thousands of programs that are produced today in Dolby Surround Pro Logic to migrate to Dolby Pro Logic II."

Neither Dolby nor SRS will maintain the status quo for long. Kraemer says SRS is looking into making its system capable of 7.1 channels.

"We're also expanding out of broadcast and into post-production later this fall," says Canavaro. Those efforts include post-production tools for AES/EBU content and Steinberg Virtual Studio Technology systems in the fourth quarter and a plug-in for Digidesign's Pro Tools TDM software in the third quarter.