05.21.2007 10:00 AM
Originally featured on BroadcastEngineering.com
NBC stations implement dialnorm

All of NBC's 10 owned-and-operated TV stations, located across the country, are now using the dialnorm specification identified by the Advanced Television Systems Committee (ATSC) to control loudness levels among disparate programming and commercials. Unfortunately for viewers, not all broadcasters are doing so. Dialnorm is the ATSC accepted method of managing DTV loudness that does not require a program-altering compressor limiter.

NBC has been at the forefront of this issue, arguing that proper audio makes for a better viewer experience and, in turn, retains the audience. Jim Starzynski, principal engineer for NBC Universal Advanced Technology, is chairman of the ATSC A/V subcommittee that has been formed to address the problem.

Starzynski said the ATSC recognized that dialnorm was not working effectively in markets across the country, and therefore established a technical subcommittee. The committee's goals are now being established, with participation from those interested in perfecting DTV audio. This includes commercial networks, PBS, equipment manufacturers and industry organizations. Within the next few months, new procedures, equipment and recommendations could be available, fixing DTV loudness problems for broadcasters and ultimately TV audiences nationwide.

In the last six months, the NBC stations coordinated between their network and station engineers to measure and adjust their digital audio encoders. They used the NBC averaging method to come up with a dialnorm figure that closely matched programming, commercial, promo and local news audio. Once analyzed and confirmed, this figure was used to set the dialnorm metadata parameter in each station's Dolby Digital encoder.

Viewers of those stations' digital channels now experience network levels and local stations levels that are similar in perceived loudness with no need to adjust the volume control.

Dialnorm allows the program provider to tag all content with loudness metadata, a stream of digital information that labels the characteristics of the accompanying audio. The transmitted information takes remote control of the viewer's home receiver and adjusts it as necessary to optimize the audio. This method is non-destructive, allows the viewer to choose control of some features and provides an accurate listening experience as intended by the program originator.

Starzynski explained that dialnorm metadata scales the perceived loudness of the dialog of all content, level shifting the audio so each transition can be smooth without compromising the dynamics of the sound.

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