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Dolby Atmos: What you need to know about the spatial audio format

From Apple Music to the movie theaters, here's how Dolby Atmos surrounds you with sound from all directions -- even above.

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The $200 Amazon Echo Studio is a Dolby Atmos-compatible speaker.

Sarah Tew/CNET

At its WWDC 2021 conference last week Apple announced "spatial audio" for its Apple Music service, and company exec Eddy Cue said it was like the transition to HD for television. What not many people realize is that this particular branch of the technology has been with us for quite a few years, where it has been, and still is, known as Dolby Atmos.  

Dolby Atmos is a popular surround-sound format, a competitor to DTS:X, and it's found in everything from the biggest commercial cinemas to home theater systems -- and now on mobile phones. While this format, also known as "immersive,"was originally designed for movie theaters, it is now used as a new way to remix and listen to music from the likes of The Beatles and Ariana Grande

While the biggest change in the cinema was the addition of height channels, Atmos soundtracks can work with many different systems, no height speakers required. Dolby Atmos can be replayed on a traditional surround system or even with a pair of headphones thanks to technologies like Dolby Virtual:X and Dolby Headphones. What Apple calls spatial audio incorporates Dolby Atmos as well as its own head-tracking technologies in products like the AirPods earbuds.

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In this explainer I'll break down how Atmos works, why height speakers and upward-firing soundbars are cool, and everything you've ever wanted to know about Dolby Atmos but never bothered to ask.

A few highlights:

  • Height channels can create a more immersive sound.
  • The best sound will be with a multispeaker setup, but even soundbars with Atmos (like the Vizio SB36512) offer a much "bigger" and more enveloping soundstage than stereo bars.
  • Ceiling speakers are great, but many companies sell upward-firing speakers that will come close in performance without the need for speaker mounting or installation.

Making sound surround

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The $450 Vizio M512a-H6 is an upcoming Dolby Atmos soundbar.

Vizio

To understand what makes Atmos different from, say, its direct predecessor Dolby Digital, let's first take a look at how sound is mixed for movies and TV shows.

Everything you hear in a movie, from the music to the voices to the sound effects, all gets mixed into specific "channels." For simplicity's sake, we'll say these channels are, as you look at them in a room, left front (L), center (C), right front (R), right surround (RS) and left surround (LS). Some more complex systems add "surround back" channels. All the low frequency booms and thumps go to the ".1" subwoofer channel. This diagram should help:

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A traditional 7.1 surround system in a theater. Lots of speakers, but only a few "channels" to direct the sound to. So a sound would come from the left "wall" not a specific speaker on that wall.

Dolby

So if two actors are speaking onscreen, that gets mixed to the center channel. When the music swells during a dramatic moment, that's usually in the front left and right channels. Zooming and swooping special effects might appear in the surround speakers. To an extent, this same mix of channels also translates to the home. After all, if you have a 5.1 speaker system, you have all those same speakers.

Except… you don't. Not exactly. Where your speakers are, how powerful they are, and increasingly, how much range each has, varies greatly compared with a decent movie theater.

Atmos, for the most part, doesn't use channels. Instead, most sounds are treated as "objects." Instead of assigning a sound to a channel (and by extension, a speaker), Atmos lets filmmakers assign a sound to a place. Not "left surround speaker" but "left rear corner." Not "pan from left surround speaker to right sound speaker" but "pan smoothly across the rear wall." Not only does this give greater flexibility, but it improves the experience in the theater and, potentially, at home. 

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With Atmos (on the right), sound designers can pinpoint exactly where in any Atmos theater they want a sound to "appear." This could be just about any place in the room, including overhead.

Dolby

Atmos is an end-to-end change in theater and home audio. The mixing is different, as we've discussed, but so is the decoding. At different theaters the number of speakers can vary dramatically, but Atmos will scale with them regardless. Most theaters have many speakers along the walls to ensure everyone gets the same-ish experience. With Atmos those speakers can be individually addressable and a sound designer can pinpoint the exact location in a theater where they want to place a sound. A smoother experience for everyone. This is represented in the image above.

This includes the headline Atmos feature: height. With speakers hanging from the ceiling, sound engineers can now move sounds seamlessly over your head and all around. Done right, it's not only more convincing than before, but also less obtrusive. It's more natural, so you're less likely to notice the special effects and more likely to stay absorbed in the movie. And that's the point, right?

So what about the home?

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Tidal offers a selection of Dolby Atmos Music titles via its app.

Sarah Tew/CNET

Theaters are great and all, but most of us watch more movies at home, even under normal circumstances. Atmos isn't even just about home theater anymore either, as Dolby has been branching the format out into music. Before Apple threw its hat into the ring, Tidal and Amazon Music offered a selection of titles that had been remixed in Atmos, and with Sony's competing 360 Reality Audio, the number of beyond-stereo tracks is still growing.

To let mobile users experience both Atmos music and movies, many newer mobile devices have a version of the technology called Dolby Atmos for Headphones. Though those are stereo-only, they're designed to simulate Atmos effects with any headphones. The tech is available for Xbox and PC as well, for $15, via the Dolby Access app.  

If you're listening at home, though, let's get this out of the way first: Obviously most people aren't going to install height speakers in their ceiling. That's fine because there are a growing number of speakers and soundbars that either feature built-in height channels or fit on top of existing models. In the case of a standard tower or bookshelf speaker you can fit a speaker model on top that has a separate, upward-firing driver. These speakers bounce sound off the ceiling to mimic "real" height speakers. I've heard quite a few of these and they work surprisingly well. Not as well as real height speakers, of course, but it works and is a far simpler option if you aren't interested in installing speakers in or near the ceiling.

Focal Sib Evo 5.1.2 Atmos speakers

The Focal Sib Evo is an Atmos-ready speaker set. Just add a Dolby Atmos receiver.

Sarah Tew/CNET

So, yes, if you want to take advantage of true Atmos surround you'll need new hardware. But Dolby Digital is still the default for everything, so this isn't a required upgrade. If you're not interested in Atmos, your gear will still work. Even if you get a brand-new 4K streamer to connect to your older receiver, the audio will still work if it doesn't have Atmos. It will just play a Dolby Digital or Dolby Digital Plus track.

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Two Atmos home setup examples.

Dolby

But if you want height channels, more channels or other benefits of Atmos, then you'll need a receiver or soundbar that can decode it and a source that provides it. (Those sources include 4K Blu-ray players, newer media streamers and some game consoles.) And you'll need Atmos content, of course, which we'll discuss in a moment. 

To the right, you'll see a couple of Atmos home setup examples. At the top, you see a setup with specially designed upward-firing speakers. Each is a traditional speaker but also has separate drivers that shoot sound to bounce off the ceiling. These are tuned so the bounced audio sounds correct to your ears. At the bottom, you see a soundbar designed to do the same. 

Atmos also lets you have a greater number of possible speakers. So how many could you have if you really wanted to go wild? Oh, 24… plus 10 height speakers. Yep, 34 speakers if you want. You don't need to do that, of course. But if you've got a bunch of spare speakers and amps laying around and a room that can fit them, go for it.

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On the left, a well-installed Atmos home theater system with four in-ceiling height speakers. On the right... good luck with that.

Dolby

For Atmos, Dolby uses a slightly different twist on the nomenclature of home systems. Traditionally a 5.1 system has three speakers up front, two on the sides or in back and a single subwoofer. If you then added two Atmos height speakers, Dolby would describe this system as a 5.1.2 system. If you see "a 7.2.4 home theater" you can deduce that it's probably got three speakers up front, two on the sides, two in back, two subwoofers and four height speakers.

All around

In addition to the gear, you'll also need Atmos content. That's actually pretty easy. If you're streaming you can find it on Amazon Prime Video, Netflix and Vudu. As we noted above, music can be found on Amazon Music Unlimited, Tidal and Apple Music. On disc it can be found on 4K and regular Blu-ray discs. It's even in a handful of video games.

Chances are if the movie is 4K, it's also Atmos -- though that doesn't mean it's in Atmos everywhere you can find that movie. It might be available with Atmos on the 4K Blu-ray, but not on Amazon, for example. Just keep in mind there won't be compatibility issues. If you buy a movie that features Atmos it will also have an audio track your current gear can play, minus the height channels.

Is it worth upgrading all your gear to take full advantage of Atmos? No. It's cool, but if you're not a home theater junkie this might be more money than you need to spend if you're not using it. When you're ready to upgrade anyway, chances are the gear you're considering will have Atmos. For example, most of our favorite receivers already work with Atmos, as do several of our favorite soundbars.

Originally published two years ago. Updated with information about Atmos Music and Apple's spatial audio.


Got a question for Geoff? First, check out all the other articles he's written on topics like why you shouldn't buy expensive HDMI cablesTV resolutions explainedhow HDR works and more.

Still have a question? Tweet at him @TechWriterGeoff, then check out his travel photography on Instagram. He also thinks you should check out his best-selling sci-fi novel and its sequel