What is Dolby Atmos and can we get it in a home theater version?

– Fred D
Cleveland, OH

Dolby Atmos is Dolby’s next generation of surround sound technology. It was introduced in select movie theatres in 2012 with the release of Brave and since then the install base has grown to several hundred theatres with over 100 movies released or announced featuring Dolby Atmos soundtracks.

Dolby Atmos represents a paradigm shift in the way surround sound material is both crafted and presented.

Rather than a sountrack being defined by a set number of channels, Dolby Atmos lets artists and sound engineers define sound by position. At playback, Dolby Atmos determines on the fly which of its many speakers to use and how to use them to present the sound as intended. This ensures that a soundtrack can be presented as best as possible whether the theatre employs the full 64 speaker system or a subset thereof, without the content creator knowing or worrying about how many channels and/or speakers there are.

To accommodate this, the speaker layout in the theatre has been revised compared to 5.1/7.1 in several ways:
? The front stage, or screen speakers, can be expanded from 3 to 5. Of particular interests to very large venues, this enables more precise anchoring of on-screen sounds, harkening back to the 70mm 6-track magnetic format many decades ago.
? The side surround arrays now extend all the way to the front of the theater as oppose to covering the rear 2/3 of the wall only.
? Two ceiling arrays are featured, both running from front to back, spaced roughly equidistant from each other and the side walls.
– Left and Right side LFE (subwoofer) channels are defined in addition to the main LFE.
? All speakers are addressed by the system individually (as oppose to groups of speakers being wired together for left-surround, right-surround, etc).

Note that this does NOT mean Dolby Atmos is a “61.3” surround sound system, at least insofar as the content is concerned. Sound engineers and artists approach a Dolby Atmos track using a beds and objects approach.

The beds consist of 10 channels in a 9.1 layout (conventional 7.1 plus the two ceiling channels) wherein the audio is mapped during playback to the corresponding speakers and/or speaker arrays: left, centre, right, left surround, left rear, right surround, right rear, left ceiling, right ceiling, and LFE. The sound engineer can also define up to 118 sound objects, that is, tracks which do not have a corresponding speaker or speaker array, but rather a defined position. It is the Dolby Atmos playback system which, at time of presentation, figures out which speakers to use and how to use them to present these various sound objects.

An example of sound object use would be when the characters on screen are reacting to a sound just off screen to one side. With traditional surround sound speaker arrays and layouts the sound would at best appear to come from beside the audience (or for those seated in the front most rows the sound might even come from behind them). With Dolby Atmos the artist can place the sound in an object track and define its position just off screen. At playback the Dolby Atmos system would map the sound to just the forward most 2 or 3 side speakers such that for all audience members the sound appears to come from in front of them, just to the side of the screen.

Dolby recently announced that they would be licensing Dolby Atmos for home theatre. As with past surround sound technology, it will be a distillation of the movie theatre system.

The first key piece to bringing the Dolby Atmos experience home will be to expand the speaker compliment. For the ceiling, ideally four but no less than two in-ceiling or ceiling-mounted speakers will be called for. Because this can be difficult or even impossible in many homes, we will see conventional speakers which include an extra channel of drivers on TOP of the cabinet firing up. Using special algorithms the sound from these speakers will be shaped such that the reflected sound off the ceiling emulates the ceiling mounted speaker arrays of the movie theatre. For those who want to keep their existing speakers, up-firing speakers will be available with the intention they be placed on top of your existing speakers. For the sides and rear, multiple speakers will be called for, though as mentioned the system will scale from few to many as may be the case in terms of hometheater size etc.

The second key piece will be AV Receivers and Surround Sound Processors with Dolby Atmos processing and an expanded number of outputs. Depending on your space and budget, Dolby Atmos in home theatre can accommodate as few as 11 or as many as 34 speakers! One of Dolby’s hardware partners is already planning a 32 channel AV Receiver.

The final piece of the puzzle is how we will get Dolby Atmos soundtracks: It will be implemented as an extension to Dolby TrueHD and Dolby Digital Plus. This means that any existing Blu ray player set to bitstream output can deliver a Dolby Atmos soundtrack to a Dolby Atmos enabled receiver or processor. Similarly, any streaming service/box which outputs either bitstream format has the potential to carry Dolby Atmos.

We at Secrets will be following very closely the development of this exciting new facet to home theatre. Look for more articles and reviews as products begin to surface.