Ask S&V

A Are there any home video releases with 7.1.4-channel sound? I find that most movies have 5.1-channel soundtracks? —J. Kevin Sexton / via e-mail

Q No, and that’s because there’s no such thing as a 7.1.4-channel soundtrack.

While regular Dolby and DTS soundtracks are channel-based (e.g., 5.1, 7.1), soundtracks produced using the new Dolby Atmos (and DTS:X) formats employ audio objects that aren’t tied to specific speaker channels.

During the Atmos mixing process, for instance, up to 128 separate objects can be positioned anywhere in 3D space. Then, when the soundtrack is played back in a cinema or home theater, an Atmos decoder is used to render the objects to the available speaker configuration. That’s why a “7.1.4” designation in the Atmos universe doesn’t indicate audio channels; it instead describes a specific speaker array used for sound reproduction — in this case, seven main speakers (left/right, center, surround left/right, and surround back left/right), one subwoofer, and four overhead height speakers, as shown in the illustration above.

Just in case you were wondering, even though Atmos and DTS:X employ a different approach to soundtrack creation than standard Dolby and DTS formats, the codecs are backward-compatible with older gear: When you play an Atmos or DTS:X disc, an older receiver will be presented with a standard 5.1- or 7.1-channel version of the soundtrack for decoding.