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Dolby Atmos: Why it's cool, how it works and how to get it

From movie theaters to your own home, here’s how Dolby Atmos surrounds you with sound from all directions -- even above.

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From the biggest commercial cinemas to the smallest of home theaters, Dolby Atmos is one of the latest ways to get surrounded by sound -- now from above! While Atmos soundtracks will work with a traditional five-speaker-and-subwoofer (5.1) system, one of its main benefits is a greater ability to work with as many (or few) speakers as you have. 

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.

Making sound surround

To understand what makes Atmos different than, 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 going around the room are left front (L), center (C), right front (R), right surround (RS), and left surround (LS). Some more complex systems add a "surround back" channel. All the low frequency noises go to the ".1" subwoofer channel.

traditional-dolby-cinema-layout

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.

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

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Except… you don't. Not exactly. Where your speakers are, how powerful they are, and increasingly, how much range each has, varies greatly compared to 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 at the theater, but improves the experience in the theater and, potentially, at home. 

dolby-atmos-pinpoint

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

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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 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?

Theaters are great and all, but most of us watch more movies at home. 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 that either feature built-in height channels or fit on top of existing models. Imagine a standard tower or bookshelf speaker, but on top is an upward-firing driver that's addressed separately. These speakers bounce sound off the ceiling to mimic "real" height speakers. I've heard a few of these and they work surprisingly well. Not as well as real height speakers, of course, but it works and it's a far simpler option if you aren't interested in installing speakers in or near the ceiling.

So yes, if you want to take advantage of Atmos 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 4K Blu-ray player with dual HDMI outputs to connect to your older receiver, it will still work if it doesn't have Atmos. It will just play Dolby Digital or Dolby Digital Plus track.

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

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Two Atmos home setup examples.

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To the right, you'll see a couple of Atmos home setup examples. At the top, 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, a soundbar designed to do the same. 

Since you've got a greater number of possible speakers, how many could you have if you really wanted to go nuts? 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.

crazy-dolby-atmos-system

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

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A handful of mobile devices, such as the Amazon Fire HD 8 and 10, also have have a version of the technology (called Dolby Atmos for Headphones) built in. Though those are stereo only, they're designed to simulate Atmos effects with any headphones.  

Dolby uses a slightly different twist to describe Atmos 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 added two height speakers, Dolby would describe this system as a "5.1.2" system. I'm not sure that will catch on, but 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 Netflix and VUDU. On disc it can be found on 4K and regular Blu-ray discs. It's even in a handful of video games including Star Wars Battlefront and Overwatch for PC and Xbox One.

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 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 nota taking advantage of 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. Prices start at around $400 for the Onkyo TX-NR575, but you'll need to spend at least several hundred more on a set of speakers such as the accompanying Atmos kit

On the sound bar side it's a little more expensive still, with the LG SJ9 costing a cool $900. As a result, if you want to get into Atmos investing in a receiver and upgrading speakers as you go is the most cost-effective solution right now.

Got a question for Geoff? First, check out all the other articles he's written on topics like why all HDMI cables are the sameTV resolutions explainedLED LCD vs. OLED 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.