Ask S&V

Q Digital high-definition broadcasting started back in 1998, but since then, only video has received a facelift, not audio. Why hasn’t DTV audio evolved to at least Dolby Digital Plus status? —David Musoke / via e-mail

A DTV audio did evolve to Dolby Digital Plus status—the Advanced Television Systems Committee (ATSC), an international organization tasked with developing digital broadcasting standards including the current system used in the U.S., incorporated Dolby Digital Plus into the ATSC 1.0 standard back in 2005. However, U.S. terrestrial broadcasters never got around to exploiting the benefits of Dolby Digital Plus (also known as Enhanced AC-3), which allows for higher channel counts and enhanced bitrate options to improve sound quality over standard Dolby Digital.

One area where Dolby Digital Plus has made a mark is with over-the-top (OTT) streaming services such as Netfl ix, Vudu, and HBO Go. New DirecTV satellite DVRs and set-top boxes are also capable of passing up to 7.1-channel Dolby Digital Plus soundtracks from content that’s encoded with it.

While audio never got a push beyond basic Dolby Digital in ATSC 1.0, the forthcoming ATSC 3.0 broadcast standard should provide a significant audio upgrade. Two audio formats have competed to be included as part of 3.0, Dolby’s AC-4 and the MPEG-H Alliance’s MPEG-H, with the ATSC ultimately recommending that specific countries or regions be allowed to select the one format that best addresses their needs.

On paper, AC-4 and MPEG-H appear to be fairly similar. Both provide object-based immersive audio with interactive features that let viewers do things like select alternative commentary tracks and independently control the level of dialogue and background sound.

They also provide dynamic range limiting and contouring to protect your ears from obnoxious ads during commercial breaks and to scale the sound appropriately for mobile devices like phones and tablets.

Which format will be selected for ATSC 3.0 broadcasting in the U.S.? No formal announcement has been made, though there have been indications that it will be Dolby’s AC-4. Meanwhile, TV manufacturers including Sony, Vizio, and Samsung have all announced plans to incorporate support for the new Dolby format in TVs starting in 2017, which is when initial ATSC 3.0 broadcasts are also expected to begin.