How Do Dolby TrueHD and Dolby Atmos Differ?

Got a tech question for Sound & Vision? Email us at AskSandV@gmail.com

Q I recently bought an Xbox One X console and have it connected to my Yamaha RX-A2050 AV receiver. When I watch Atmos demo videos using the Dolby Access app on the Xbox, my AVR’s front-panel LED display reads “Dolby Atmos.” I get the same result when I watch Netflix shows with an Atmos soundtrack. When viewing Ultra HD Blu-rays with Dolby Atmos soundtracks, however, the receiver’s front panel will read “Dolby TrueHD.” Are Atmos and TrueHD the same thing? —Hans Furey / via e-mail

A No, they’re not. Dolby TrueHD is a lossless audio codec that supports up to eight audio channels on Blu-ray Disc. Dolby Atmos soundtracks, in contrast, consist of audio objects — up to 128 of them — that are mixed in a 3D soundfield during the production process. When the soundtrack is played back in a movie theater or home environment, the audio objects are rendered by an Atmos decoder to the available speaker set, which includes overhead ceiling speakers.

While Dolby Atmos and Dolby TrueHD are two separate soundtrack formats, Atmos data on Ultra HD Blu-ray is actually an extension to TrueHD that is folded into the bitstream to maintain backwards compatibility. Here’s how that works: If you play a disc with an Atmos soundtrack, the Atmos extension data is decoded by an Atmos-compatible receiver. If your receiver isn’t Atmos compatible, the extension data is ignored and the soundtrack is decoded as regular Dolby TrueHD.

Now that we’ve covered the differences between Atmos and TrueHD, let’s discuss your Xbox One X. There are documented issues on the Xbox support site of Microsoft’s Blu-ray player app defaulting to TrueHD output when playing discs with Atmos soundtracks. Microsoft regularly updates their app (a patch was recently done to correct too-high black levels when playing discs with high dynamic range video), so your first step should be to make sure you’re running the latest version. While you’re at it, also make sure to update the firmware on your receiver: Atmos playback problems with the Xbox One X are reportedly associated with specific receivers and soundbar models, so Yamaha may have a related fix in the works.

X