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DTV Audio Moves Towards Consistency

LAS VEGAS, NV—A production seminar hosted by the DTV Audio Group during the recent NAB Show focused on the operational and engineering challenges of optimizing and standardizing the 5.1 DTV audio format associated with television’s default production format, HD.

LAS VEGAS, NV—A production seminar hosted by the DTV Audio Group during the recent NAB Show focused on the operational and engineering challenges of optimizing and standardizing the 5.1 DTV audio format associated with television’s default production format, HD. Moderated by DTV Audio Group executive director and independent media technology consultant Roger Charlesworth, the event was sponsored by Blue Sky, Dale Pro Audio, Dolby Labs, Linear Acoustic, Stagetec and Wohler, and produced by the Sports Video Group.

Maintaining production format compatibility in an increasingly fluid delivery environment is critical, to be sure, and the event’s presenters and panelists offered valuable real-world advice on the subject. But looming over everything was one topic: loudness.

Mark Richer, president of the Advanced Televi s ion Sys tems Committee, reported that Annex J of the ATSC’s A/85 Recommended Practice is close to a member vote. It gathers together the essentials for maintaining loudness for the FCC to reference in relation to the Commercial Advertisement Loudness Mitigation (CALM) Act. Annex K, which addresses non-AC-3 codecs, will follow, he said.

No one knows yet what action the FCC might take against infringing stations, Richer continued. “I don’t think they have the wherewithal to inspect every station” for compliance, he said, but also suggested, “They’re going to be serious about it if there are any complaints.”

Bob Dixon, director of sound design and communications for the NBC Olympics Unit, offered practical advice for mixing to a target loudness measurement. “Loudness is not hard,” he considered, and maintaining a consistent level makes no real difference to the mixer’s job. Loudness meters were put into every truck at the Olympics; once the reference was set and the listening level adjusted, the correct loudness levels were easily maintained, “just by checking the speedometer,” he reported.

Charlesworth and the members of the DTV Audio Group have long advocated for the idea of single-threaded delivery, whereby audio is produced in 5.1 throughout the plant and is downmixed as necessary by equipment in the home. This idea was picked up by Tomlinson Holman, professor of film sound at the University of Southern California, in his observations on the current state of TV audio. “Kill stereo,” he exhorted; the format was never used in film, which instead has utilized at least three channels (LCR) across the front, he pointed out.

It’s not too difficult to maintain loudnes s level s , even wi thout technology, Holman observed, noting that he tells his students to “mix with their ears. [They] can set a level of dialog and maintain it consistently; it’s really quite remarkable.”

There were a number of technology presentations, including one by Tim Carroll of Linear Acoustic, who warned against strict adherence to loudness regulations at the expense of audio quality. The easy answer to loudness control might appear to be the application of processing. But Dolby’s Dialog Intelligence, licensed by Linear Acoustic for its LQ-4000 meter, offers consistent measurements, said Carroll, and reduces the need to apply potentially harmful processing.

Carroll half-jokingly professed to be “getting out of the audio business.” Instead, he said, “I’d like to sell… processors that are adjusted properly with things that use metadata.” A hybrid approach (as found in his company’s award-winning Carbon technology products) that offers bypassable processing is the best way to achieve quality audio that complies with loudness regulations: “When it comes to loudness control, think globally but act reversibly,” said Carroll.

Jeff Riedmiller, director, sound platform group, for Dolby Labs, announced that the company’s loudness estimation and correction tools will soon be available for general licensing. The core dialog gating technology in Dialog Intelligence will be made available at no cost, he said.

Michael Abbott, audio coordinator for the Grammy Awards telecast, reinforced the single-threaded idea during a panel discussion on end-to-end 5.1 strategies for fast-moving productions. “The networks are requesting only 5.1,” he reported. If there is an LtRt mix delivered, it’s likely for backstage use or for checking continuity.

But it can be difficult to get show producers to understand the workflow and convince them of the value of 5.1, he said. “There’s a misconception that it’s going to cost them extra money.”

“I create 5.1 onsite,” revealed Fred Aldous, senior mixer for Fox Sports. But problems can arise with integrating legacy stereo material: “How do we deal with that?”

Some of the problems associated with standardizing the various facets of DTV audio were highlighted in a panel moderated by Tom Sahara, VP operations and technology for Turner Sports and the chairman of the DTV Audio Group. For example, SMPTE 2035, the EBU recommendation for track allocation for file exchange, lists 41 cases just for 8-track VTR systems, and 12-track cases will soon be added. With MPEG-4 freeing up bandwidth and allowing 16-channel HD-SDI audio the prospect becomes more complex, but, he said, “The technology is here.”

DTV Audio Group