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Dolby Features AC-4/Atmos At IBC Show

AMSTERDAM—Dolby Laboratories’ next-gen AC-4 audio delivery system, which was engineered to deliver high-quality television sound, along with the Dolby Atmos surround sound system dominated the company’s IBC Show stand this year.

Mathias Bendull

Mathias Bendull, Dolby’s vice president of multiscreen services audio, described AC-4 technology and some of its many benefits to members of the press in a Sept. 17 stand briefing.

“[As part of the audio encoding process] we identify the frequencies which are dialogue and put a flag there to identify these frequencies,” he said. “The decoder recognizes the flag and can boost those specific frequencies and duck the others so that you can understand the dialogue a little more clearly.” He noted that performing this speech frequency identification as part of the encoding process brought with it several benefits.

“You could do the same thing [at] the TV,” he said. “But you would have to have a stronger chip set; you would also have more latency. You want to avoid these things and [do] as much as possible upstream.

“AC-4 supports the ideal scenario where you create the dialogue as individual audio elements and allow the consumer to distinguish the ratio of the dialogue to the music. We have dialogue intelligibility in the existing workflows, so we take the existing 5.1 mixes and through an intelligent encoding process create better intelligibility on the playback device.”

He observed that it would be fairly easy for television receiver manufacturers to implement a button marked “improve dialogue.” This would instantly boost intelligibility of commentary or other dialogue for consumers who might have a hearing disability, or just want to minimize some of the music and sound effects being transmitted.

Bendull said that some of the major television receiver manufacturers are beginning to support AC-4, including Samsung and LG, and that two European broadcasters—Spain’s RTVE and France Télévisions—have been airing AC-4 audio.

“RTVE is using one of their channels [in Madrid] to deliver AC-4. The other one is in Paris, and that one has been on the air for almost a year-and-a-half now transmitting an AC-4 combination with HD, or sometimes 4K using Dolby Vision.”


Rob France, senior product marketing manager at Dolby, provided information about another Dolby technology, the Atmos surround sound system.

“Dolby Atmos for live sport is really about bringing [home] the passion of the game in ways that the vision alone just can’t [deliver],” said France. “Audio is the only way you can connect the fans with the crowds that are there [in the sports venue] in a really compelling way.

He explained that crowd noise, the sound from the kicking or striking of a ball, public-address audio, all contribute to a spectator’s experience when attending sports events in person and producers of such events for television employ all of these audio elements, and more, to bring the “live viewing” experience to the home television consumer as fully as possible. He added that live sports audio production differed from that in most other types of programming. 

“First, you are listening [mostly] to scene-based rather than specific individual sounds. [And] because of the time pressure and the complexity in producing a live event, you really have to look at a simpler way of producing audio,” noting that Atmos technology enables broadcasters to more easily do this and enhance the home viewer’s experience.

“[U.K. broadcasters] BT Sport and Sky Sports are producing regular football games in Dolby Atmos. BT Sport launched their Dolby Atmos broadcast as the world’s first broadcaster to do live content on a regular January of this year. Sky Sports recently launched the start of its season [with Atmos] about one month ago, and between them, they’re going to deliver about 200 events and matches through next year.”


As the audio use cases described centered on European deployments, France and Bendull were asked about U.S. broadcasting applications, specifically in connection with the pending ATSC 3.0 broadcast standard.

“You’re seeing it on Netflix and other services,” said France. “[And] we’ve see trials in the past with broadcasters in the U.S. as well. ATSC 3 will drive a lot of the content production, and it will naturally bring along all of the features of AC-4 such as the dialogue enhancement, which is absolutely key. Premium content will be mixed in Dolby Atmos…giving more features. Ultimately, ATSC 3, I think, will be one of those things that [will] cause content to be created in a better way.”

“Within ATSC 3, the U.S. broadcasters have decided to use AC-4 for the next-generation transmissions,” said Bendull. “The CTA…has followed that recommendation in their recent decision about next-generation ATSC 3 TVs as well, and we are currently engaged with a number of networks in the U.S. to launch trials in 2018 to test that, as we have done in Europe.”

(AC-4 audio has been adopted by the DVB Project and standardized by the European Telecommunications Standards Institute. It was approved on Feb. 23 this year as one of the next-generation audio transmission standards for use in ATSC 3.0.)