Dolby AC-4: The Next Step For U.S. Broadcasting?

FKT Magazin 3/2018

This major decision came after the Federal Communications Committee (FCC), America’s TV broadcasting governing body, voted unanimously to allow American broadcasters to voluntarily deploy the new ATSC 3.0 standard to facilitate next-generation TV services (higher quality video, IP streaming and “immersive” audio services). 

The FCC rules do not mandate a specific audio system, a U.S. broadcaster could use either AC-4 or MPEG-H, but the later may not be receivable on some consumer devices made for and sold in North America, according to Mark Richer, president of the ATSC. MPEG-H has been designated for use in South Korea by that country’s Telecommunications Technology Association (TTA) and will be used for this year’s Summer Olympics, which will be distributed terrestrially in the A/300 ATSC 3.0 System Candidate Standard system.

Richer noted that in May of 2016 the North American Broadcasters Association (NABA) officially recommended Dolby AC-4 as the preferred audio codec for OTA broadcasting. Therefore, broadcast organizations in North America have selected A/342, Part 2 (AC-4) while the TTA has selected A/342, Part 3 (MPEG-H) for use in South Korea. Both audio systems are now part of the overall ATSC 3.0 specification.

But, for North American Broadcasters, Dolby’s AC-4 is the format they will use to compress and send audio content from a myriad of sources. That’s assuming they don‘t continue to send 5.1 or stereo mixes to consumers’ homes.

For the industry, it took more than four years to get to this point. Proponents say AC-4 represents a fundamental change in the distribution of audio signals, replacing traditional broadcasting methods with a state of the art system that will make OTA broadcasters more competitive in today’s highly fractured landscape.

The goal with either audio codec is to significantly improve upon the capabilities of the current multi-channel broadcast digital television audio system and provide consumers with a more compelling, personalized and immersive experience. ATSC 3.0 audio “personalization” will include enhancements to the control of dialog, use of alternate audio tracks and mixing of assistive audio services, other-language dialog, special commentary, and music and effects.

ATSC 3.0 audio also will support both the normalization of content loudness and contouring of dynamic range, based on the specific capabilities of a user’s fixed or mobile devices and their unique sound environments. 

Immersive audio (AC-4) signals envelop the listener with precise sound source localization in azimuth, elevation and distance, and provide an increased sense of presence. These features can be supported over the listening area, without the need for a large number of physical speakers.

Dolby has said its AC-4 audio compression system provides a practical, scalable and flexible set of tools to enable the efficient production, distribution and delivery of consumer broadcast experiences for all audiences today and in the future. This solution spans content creation, distribution and consumer delivery. 

To install the new Dolby Labs system, stations will have to buy a new video encoder with Dolby AC-4 software built-in. (Many manufacturers have shown prototypes at the various trade shows and many expect new models to be on display at this year’s NAB show.) Stations can send one AC-4 stream that contains an immersive experience that capable of being personalized (e.g., you can pick specific announcers or different camera views during a major live event) to mobile devices, the living room and computers and the Dolby software-based decoder is smart enough to adapt to the specific device it is bring received on. And you can do it in less bandwidth. In AC-3, stations could send multichannel 5.1 encoded content at 384 kbps. In AC-4 they can now deliver a great 5.1 experience at less than 100 kbps. So that bandwidth saving s can be used for other things.

Look for the next generation of 4KTVs and other media players to include a Dolby AC-4 decoder built-in. In fact, at the recent CES Show in Las Vegas (in January) Dolby AC-4 was already being implemented by a wide variety of system-on-a-chip (SoC) designers, professional partners, and consumer electronics manufacturers like LG Electronics, Samsung, and Sony. [If you’ve got a Sony TV from 2017, you’ll be pleased to know that Sony plans to add Dolby Vision to the higher-end models from last year via an upcoming firmware update.]

In anticipation of the Summer Olympics, South Korean broadcasters like SBS have begun real-world ATSC 3.0 broadcasts, using the MPEG-H audio system developed by the Fraunhofer Institute, Technicolor and Qualcomm. At the CES Show Fraunhofer showed its MPEG-H Audio technologies and products that are being used for South Korea’s terrestrial 4K TV broadcast service.

Dolby’s AC-4 codec has also been tested at RTVE, in Spain, TVF, in France and KQED, the PBS member station in San Francisco, California. All remain on the air with test signals and have reported positive results.

The issue now is how long these new codecs will get in the hands (and living rooms) of consumers both in North America and abroad. Many predict a situation, much like today, in which many broadcasters will continue to send out stereo while a few will distribute AC-4 or MPEG-H-encoded content. The A/300 ATSC 3.0 Standard system makes accommodations for this.

Look for more live demonstrations of the new audio technology at the upcoming PBS Technical Conference (held two days prior to the 2018 NAB Show) as well as the NAB Show exhibit floor within the Dolby and Fraunhofer booths, in some other partner booths, as well as within the ATSC Pavilion. 

It’s clear that while the ATSC 3.0 system is slowly rolling out in the U.S., a lot of people are eager to start testing AC-4 in their own regions and experiment with its many audio signal possibilities. With each passing month the industry is learning more and more about how to best implement it in a manner that will prompt consumers to use the codec’s immersive features and alternate audio tracks as part of new revenue-generating services.

Only time will tell whether AC-4 or MPEG-H takes off with broadcasters (and consumers), but these next-generation audio codecs offer great potential for a wide array of new services to those willing to take the next step in audio processing. Is your company brave enough to try?