Dolby Atmos for the home

Audio Media attended a Dolby Atmos Everywhere event on 13 August, experiencing Dolby Atmos for the living room in the home theatre at Dolby House, Soho Square.

Dolby Atmos is based on the notion of audio objects, which could be any single thing, positioned in a specific place in the room rather than played from the front of the screen. Each of the objects carries metadata, so an object is monophonic and has no placement information. It is the metadata that carries the placement, how that sound moves through the scene, and the volume at which it plays.

So how is the company bringing Dolby Atmos from the cinema (which has real overhead speakers, lots of speaker opportunities, and massive rendering power) to the home? A Dolby Atmos cinematic presentation can carry up to 128 concurrent objects at one time. In realtime the Dolby Atmos Cinema Processor takes the metadata and positions the objects with an understanding of what the speakers are, where they are in the room, how configured those speakers are, and the size of the room etc. That means a smaller room with less speakers, provided it has a Dolby Atmos Cinema Processor, will render exactly the same.

In the cinema, a full-length movie has several gigabytes of audio information and metadata. To make that work in the home Dolby had to develop spatial coding, which is a way that the data is simplified to more efficiently deliver the objects in updated versions of the company’s Dolby TrueHD or Dolby Digital Plus bitstreams. The crux of the Dolby Atmos Cinema Processor working with the spatial coder is a Dolby Atmos audio renderer for AVRs or preprocessors etc.

Authoring/encoding houses specify how much spatial coding goes on a Blu-ray depending on how much they want to get the size of the finished file down. The solution has a high degree of backwards compatibility. A legacy amplifier sees the bitstream on a Blu-ray disc and ignores the spatial coding. There is no height and there is not as much movement, but all the sounds are still there because embedded in the metadata is a copy of the object that needs moving with no metadata.

Dolby also did a little bit of reverse engineering of how the brain interprets overhead sound. Realising ceiling speakers at home might be impractical for many reasons; the company emulated them with up firing speakers, speakers at a slight angle that aim sound up to the ceiling that comes down to the listening section of the room. The Dolby Atmos-enabled speaker is something that the company is working on with speaker manufacturers as a licensed technology. It includes a hardware design, characteristics of the driver, plus some filtering and processing.

In the screening room Dolby installed overhead and up firing speakers, sets of which could be toggled between. At waist height the room has seven KEF floorstanding speakers and two Bowers & Wilkins subs. The room has four speakers in the ceiling and four Dolby Atmos-enabled up firing speakers made for the company by KEF. Five mics were used to do the collaboration of this room. Dolby worked with consultants Munro Acoustics, which acoustically treated the room. Dolby has also tried five speakers at waist height in a slightly smaller space, with two overheads or up firers.

Dolby has worked on the technology for more than a year. “Atmos has been the most successful cinema technology we’ve ever done,” said JJ (Jonathan Jowitt), evangelist, content and e-media solutions, Dolby Europe Limited. “It’s been a fascinating process converting the cinema experience into what we can deliver in the home. We’ve been busy all this year making sure the tools to author Dolby Digital Plus and Dolby TrueHD with an Atmos spatial coding inside have started to be distributed around to the post-production houses and the content encoding houses. That’s taken longer than we really wanted but it’s in place and it’s all happening now.”

Atmos titles will start to be seen on Blu-ray in the coming months.

Dolby is additionally working on the technology for mobile.