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07.08.2008
Originally featured on BroadcastEngineering.com
Carroll sets out to bust DTV audio myths

A few weeks ago, a press release from Linear Acoustic announced the kickoff of a nationwide tour to bust commonly held myths among broadcasters about DTV audio.

That seemed like a worthwhile goal given the continuing saga of broadcasters dealing with inconsistencies in loudness and lip sync problems. Add to that questions broadcasters have about what to do with HDTV’s 5.1 surround-sound channels, and it only seemed appropriate to speak with Tim Carroll, president and founder of Linear Acoustic, about the tour and the DTV audio misconceptions the company is finding.

HD Technology Update: About a month ago, Linear Acoustic announced its nationwide Myth Busters Tour aimed at addressing DTV audio misconceptions. Before you began the tour, what did you view as the top three or four DTV audio misconceptions? Are they playing out as the top misconceptions as you make visits during the tour?

Tim Carroll: Stations are realizing the simple fact that they have processing for analog television and need processing for digital television as well, and this new breed of processor must be able to handle loudness control for stereo and surround-sound programs, support metadata and provide ATSC-required audio encoding. Having it all in a carefully tuned integrated box makes it plug-and-play and far more cost-effective — this eliminates the need to make a hodgepodge of cards work or using old-style processing based on the completely different world of analog broadcast.

HD Technology Update: What are the top sources of DTV loudness problems? What strategy or strategies do you recommend for correcting them?

Tim Carroll: In the U.S., we have found that loudness problems crop up in many areas but seem to be concentrated at the local stations, which are burdened with integrating content from network and a myriad of local sources. Our strategy is to get loudness correct at each stage. By focusing on the different needs of ingest, local production and transmission, loudness is fixed, and the quality of the content is preserved. This is in harmony with the direction of the ATSC subcommittee on loudness, chaired by Jim Starzynski of NBC.

HD Technology Update: To what degree are broadcasters responsible for the loudness issue? How responsible are cable, satellite and IPTV headends for the issue?

Tim Carroll: According to ATSC specification A/53B Section 5.5, the proper loudness of programs must be indicated, thus allowing decoders to normalize program loudness. FCC rules in CFR 47 Section 73.682 state that as of Feb. 1, 2005, “transmission of digital television (DTV) signal shall comply with the standards for such transmissions set forth in ATSC Doc. A/53B.” This makes it the law of the land for FCC-licensed terrestrial broadcast TV stations. As cable, satellite and IPTV headends are receiving these terrestrial signals by some means, it seems that if the station is compliant, then retransmission should be smooth.

HD Technology Update: Lip sync problems can be a major problem in DTV. Is it sufficient to identify and compensate for signal processing delays introduced throughout the broadcast chain (encoding, decoding, etc.), or is there a bigger issue in play, specifically something about MPEG-2 that inherently is responsible for the drift?

Tim Carroll: Like loudness, lip sync also needs to be fixed at each stage — catching it at the end is ineffective and will still result in uncorrectable variations. As for MPEG-2 issues, while the jury is still out, there has been some recent compelling evidence to suggest that there may be issues in certain implementations of MPEG-2 encoding itself.

HD Technology Update: Even if broadcasters offering local HD newscasts choose to continue offering stereo — at least initially — what steps should they be taking to plan for a 5.1 surround eventuality? Or, will there be no place for 5.1 surround in news?

Tim Carroll: There are many good reasons for 5.1 channel audio in news. Even if the mix is as simple as dialogue in the center and natural sound in left front and right front, this is far more compelling than mono sent only to the center channel and is hardly more complex to create. Upmixing and special processing can even help automate this, so that mixers do not need to change practice and can ease into 5.1 as their markets demand.

HD Technology Update: What else would you like to add?

Tim Carroll: It amazes me that the ATSC standard was adopted nearly 13 years ago, and we are now down to the wire with analog cutoff being very close at hand with so many loudness issues that remain. As it is imperative that a TV station have protection processing for its analog path, it is equally imperative that the digital path be given the same treatment with modern tools designed specifically for this task. We will continue to develop products that not only solve these problems simply and logically, but also do so within the budget of every station.

Tell us what you think! HDTU invites response from our readers. Please submit your comments to editor@broadcastengineering.com. We'll follow up with your comments in an upcoming issue.


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