HOW IT WORKS
Dolby Atmos audio format explained
Chances are you’ve experienced Dolby Atmos without even knowing it: the technology was launched in 2012 and is used in thousands of cinemas. It’s also part of the Dolby Cinema home theatre format.
Dolby Atmos is a way of delivering incredibly accurate, lifelike audio. It’s mainly used in films but it can do amazing things in music too: REM’s recently remastered Automatic For The People was also remixed for Dolby Atmos with what singer Michael Stipe described as “breathtaking” results.
Dolby Atmos takes surround sound to the next level, quite literally. Where traditional surround sound systems put audio in front, beside and behind you, Dolby Atmos puts it above you too. For example, let’s say you’re watching a film where bullets are flying overhead. With normal surround sound, the sound of those bullets will come from left, right, front or back – but it won’t come from above you. With Dolby Atmos, it does.
Dolby Atmos isn’t audio. It’s information about the audio, information that takes the existing audio data and tells the app or device what to do with it. For now Dolby Atmos sits on top of two different kinds of surround sound audio: Dolby TrueHD, which is only currently used on Blu-ray Discs, and Dolby Digital Plus, which is used by streaming services and on devices such as Apple TV. If your device or app understands Dolby Atmos it’ll read the data and deliver the Dolby Atmos experience. If it doesn’t, it’ll deliver standard surround sound.
Surround vs Atmos
You’re probably familiar with surround sound setups being described as 5.1 or 7.1 surround. The numbers tell you how many audio channels there are; the .1 means a subwoofer for bass. Bass frequencies aren’t particularly directional so it doesn’t really matter where you put your subwoofer(s).
With a 5.1-channel surround sound setup there are five main audio channels in addition to the sub bass: front left, front centre, front right, rear left and rear right. With a 7.1 setup there are another two channels, so you have front left, centre and right; centre left and right; and rear left and right. In a typical home setup you’d have one speaker per channel, so for example with a 5.1 surround sound system you’d have front left and right speakers, a centre speaker and two rear surround speakers. In a cinema, you’ll usually have
Whether it’s a helicopter or harmonica, the result is extraordinary
a 7.1 setup with multiple speakers for each channel but, no matter how many speakers you use, there are still only seven main audio channels – so every speaker hooked up to, say, the rear left channel will play exactly the same thing at exactly the same time.
Dolby Atmos does things differently. It adds extra audio channels for overhead sounds, expanding the sound stage from 2D to 3D. And it gives sound mixers Audio Objects so that they don’t just pick a channel for an instrument or effect, they decide where in the 3D space it should be; the Dolby Atmos processing then works out how much of that instrument or effect to put into each channel to deliver that perfect positioning. Whether it’s a helicopter or a harmonica, the result is rather extraordinary.
The UK’s first Dolby Atmos cinema had 400 speakers, which is probably overkill for your front room. A standard Dolby Atmos setup for the home would be a 10-channel, 7.1.2 setup with seven surround speakers (front, side and rear), one subwoofer and two Dolby Atmos speakers; a fancier setup – and the setup Dolby recommends – doubles the Dolby to deliver 7.1.4 using four dedicated Dolby Atmos speakers.
Bouncing the sound
If your speakers aren’t directing audio from above you or bouncing it off the ceiling though, you won’t get the effect of Dolby Atmos’s height channels. Atmos speakers are specifically designed to send audio upwards to bounce it off the ceiling and back down to where you are. With Dolby Atmos soundbars, the standard speaker array is supplemented with upwards-firing speakers for that allimportant immersion.
Dolby Atmos is now supported fairly widely: in addition to Apple’s own TV app, you’ll find Dolby Atmos soundtracks in Disney+, Netflix and Amazon Prime Video content. For Netflix, you’ll need to be a subscriber to its Ultra HD (4K) plan with your streaming quality set to High or Auto. You can’t just search for Dolby Atmos titles in these services; you need to look for the little logo next to the film or programme’s description.
As you’d expect, the titles offering Dolby Atmos tend to be action-packed blockbusters as there isn’t much call for perfectly positioned audio in films where the only moving element is somebody’s teacup. That means films such as John Wick 3, The Last Jedi, Deadpool, Black Panther and the final Avengers movie. But there are other interesting choices too such as the epic Gravity and the joyful La La Land, while edge-of-the-seat chillers such as Jordan Peele’s Us are even scarier. Carrie Marshall