By Brett Crockett, Senior Director of Sound Technology Research
If you’ve been to see a movie in Dolby Atmos®, you know that it’s a big experience. Some Dolby Atmos cinemas have as many as 64 speakers, including a number on the ceiling. If there’s an important battle scene, you may hear shouting to your left, gunshots to your right, and a fighter plane strafing overhead. It’s like you’re inside the movie.
The Dolby Atmos experience is so big and enveloping that many people have wondered how we could possibly bring it to living rooms. And believe me, as Dolby’s senior director of sound technology research, I wondered the same thing when my team was given the assignment two years ago to develop Dolby Atmos for home theaters.
I’m proud to say that we were able to meet that challenge. Movies mixed in Dolby Atmos will be released on Blu-ray Disc™ and through streaming video providers this fall. And receivers and speakers that will recreate Dolby Atmos in the living room are coming to audio retailers now. (Check out my previous blog post for more about the science behind Dolby Atmos enabled speakers.)
For a researcher like me, figuring out a way to extend Dolby Atmos to home theaters has been a fascinating process, in part because we’re working with a whole new audio technology. Dolby Atmos is different from any cinema audio system that preceded it because it is based on the concept of audio objects. Each sound in a scene—a car engine revving or a child crying—can be a separate object. Filmmakers can precisely place those sound objects in three-dimensional space around you—over your left shoulder or above your head, for instance—and determine where they should move as the scene progresses.
An individual scene can have as many as 118 audio objects. And each object is accompanied by metadata, which includes information about its location and movement. That’s a lot of information.
In the cinema, that audio data is fed to a sophisticated Dolby Atmos cinema processor, which decides, in real time, how to use that movie theatre’s unique layout of speakers to recreate each of the audio objects in the right location. Whether the movie is playing in a huge 3,000-seat theatre with 64 speakers or an intimate screening room with many fewer speakers, the placement and movement of sounds is the same.
But object-based audio is incredibly flexible and adaptable. You can also experience it with a handful of speakers in a living room.
From cinema to living room
How do we translate Dolby Atmos sound from a cavernous cinema filled with sophisticated speakers to a modest living room home theater? The first thing to know is that we use all the audio objects created for the cinema experience in the home theater. Nothing is lost.
Some people have found that hard to believe. But really, there’s no other way. Each sound in a movie scene adds to its meaning. We’d no sooner leave out some sounds than we would cut out some characters. Both are essential to the story.
Still, transmitting all of a movie’s audio objects is a challenge. How do we fit all those audio objects on a Blu-ray Disc or in a streaming video signal?
We developed a new technology called spatial coding. This new encoding method takes into account the location of audio objects to more efficiently encode them. That sounds easy, but developing the technology took years, and without it, Dolby Atmos for home theaters wouldn’t be possible. Through spatial coding, we’re able to deliver full Dolby Atmos soundtracks in the updated versions of Dolby® TrueHD, the audio format used in Blu-ray Disc media, and Dolby Digital Plus™, which is used by streaming video services.
So now we have a movie’s audio objects captured on a Blu-ray Disc or in the streaming version of a movie. But it’s also vitally important to us that they play back in your living room in just the way the filmmakers intended. The key to that part of the puzzle is the object audio renderer found in every Dolby Atmos enabled receiver or pre-processor.
The brains of a Dolby Atmos home theater
The renderer is the brains of any home theater—and with Dolby Atmos, that brain has gotten a lot smarter. In fact, it’s based on the same technology as the cinema processor in a Dolby Atmos movie house.
In channel-based systems, the renderer is a simple order-taker. The soundtrack calls for a sound to play through a specific channel, for example, the right surround speaker, and the renderer sends that sound to that speaker.
In a Dolby Atmos system, the renderer is more like a sophisticated general. When you set up your system, you tell the renderer how many speakers you have, what type they are, and where they’re located. The soundtrack describes where a sound should originate and where it should move. Just as in the cinema, the Dolby Atmos renderer decides on the fly exactly which speakers to use to faithfully recreate what the filmmaker intended.
It’s the intelligence of the Dolby Atmos renderer that produces home theater sound that’s incredibly precise and lifelike. Whether it’s an arrow whizzing inches over your head or a hummingbird buzzing its wings over your right shoulder, you’ll know exactly where that sound is—even if you can’t see the object on the screen. (You can get more details about Dolby Atmos for home theater in our white paper.)
I think you’ll find that a Dolby Atmos home theater does an amazing job of reproducing the experience of watching a Dolby Atmos film in a huge cinema. But you don’t have to take my word for it—in the coming months, retailers like Magnolia Home Theater and Magnolia Design Centers in the United States, Future Shop in Canada, Sevenoaks Sound and Vision in the United Kingdom, and AVAC Corporation in Japan, among others, will have Dolby Atmos demo rooms where you can hear the technology for yourself. I think you’ll be impressed.