What is Dolby Atmos? How immersive audio actually works

Atmos isn’t multichannel audio. Yes, an Atmos setup can use a lot of speakers, but that doesn’t make it the same as 5.1.

Picture this. An engineer mixes a track in Atmos on a 7.1.4 speaker layout. Then they play that same mix back on a 9.1.6 system, then on 7.1.2, then 5.1.2, then 5.1, then in stereo, and finally as a binaural version over headphones.

Which of those is Atmos?

All of them.

They’re all the same Atmos mix. Before Atmos and other immersive formats caught on, different playback layouts were basically treated as different formats. Immersive audio changes that. Changing the speaker layout you listen on doesn’t change the format.

Atmos is an adaptive format. Think of it as a container that holds all those layouts and treats them as one.

The concept of channels in Dolby Atmos

Here’s a situation that can come up in Atmos.

You have a multichannel bus set to 9.1.6. One of its channels is called Left Wide, and you send a signal to it. But the layout you’re actually listening on doesn’t have that channel, so the signal plays back through the two nearest speakers, creating a phantom image right where Left Wide would be.

The channel exists in the mix, but depending on the playback layout, there may be no physical speaker tied to it at all. On another layout, there might be a speaker that reproduces it directly.

The renderer is a separate story. The renderer, the Atmos engine that does all the “magic”, has 128 channels of its own, and those are a completely different kind of channel.

Picture the renderer as its own DAW with a ceiling of 128 tracks or buses. You spread your mix across those 128 tracks, and the renderer then sends that audio out to a specific speaker system.

This trips people up at first, because it isn’t always clear which “channel” someone is talking about.

What is a bed in Dolby Atmos?

The Atmos renderer supports 128 channels, and those channels are split between two kinds of audio component: objects and beds.

So what’s a bed? Think of the everyday buses you already use in a DAW: stereo, mono, 5.1, 7.1, 7.1.2, and so on. Say you’re working in 9.1.6, you’ve got a handful of signals, and you decide this group only needs the left, right, center, and two surround channels. You can build a 5.0 bus, assign it as a bed, and route those signals through it.

Pan a signal inside that bed and it can only reach that limited set of channels. The other speakers in your layout are off-limits.

A mix can have a single bed or several.

You might group your drums into their own bed, for instance, and run multichannel processing on it: multichannel EQ, compression, whatever, exactly like you’d treat a normal group bus. You could set up one bed for harmonic instruments, another for all the vocals, or just run everything through a single bed. There are no hard rules for how to use them in a music mix. The real advantage of beds is the multichannel processing, which gives you tighter control over the mix’s dynamics.

There’s a catch, though: beds have a ceiling. The largest bed you can build in Atmos is 7.1.2. So if your entire mix lives inside a bed like that, it simply won’t reach all the speakers in a bigger layout like 9.1.6. You can work around this, but there are caveats, and that’s a topic for another time.

What are objects in Dolby Atmos?

An object is a mono or stereo audio component, and unlike a bed, it can use every speaker in any layout. An object can be a single track or a bus with several tracks grouped under it.

Got six rhythm-guitar tracks? Group them into one stereo bus and make that bus an object, so you don’t have to turn every single track into its own object.

The beauty of objects is that they scale without limit. Here’s how that plays out: you’re mixing on 7.1.4 and you pan an object somewhere between the left front and the left surround, a speaker off to your left. On 7.1.4, the object uses the left front and left surround together. Move to 9.1.4 and there’s now a dedicated speaker that can reproduce it on its own.

In theory, even if you had a layout like 200.25.10, if it ever exists, objects could use every speaker in the room.

If you want your Atmos mix to stay as flexible as possible and scale cleanly past 7.1.2, you can’t avoid objects.

That doesn’t mean you should make everything an object. For plenty of sounds, especially low-frequency or static ones that don’t need to reach every speaker, there’s nothing to gain. Knowing when to reach for an object versus a bed comes with experience, because every mix throws up its own situations, and the fastest way to learn is hands-on, experimenting while you mix.