So, what is it?
Music mixed in Dolby Atmos.
So, like, surround sound?
Yes, with an asterisk we’ll come back to. Most surround systems use multiple channels: the original Dolby Surround used four (left, right, center, and rear), then moved to five (splitting the rear into left rear and right rear), and a few Even More Channels variants. Dolby Atmos, though, doesn’t have channels. Instead, it assigns audio tracks to “audio objects,” which have three-axis positions in virtual space. Each object has metadata that says, “this object should sound like it’s coming from a point this far between the left and right walls, this far between the rear and front walls, and this far between the floor and ceiling.” When you play the Atmos soundtrack, the decoder—called a “renderer” by Dolby—knows how many speakers it has available in the room and their positions within 3-D space, and it maps the audio objects onto specific speakers at specific values. It’s remixing the audio to match the playback environment on the fly, with as high fidelity to the original audio object positions as possible.
That’s pretty cool! What about, uh, not movie theaters?
The home version of Atmos works essentially the same way, just mapping to fewer speakers—typically just five, although you can get fancy and go up to eleven.
Is that a Spinal Tap reference?
If you want.
So how do you get all that fancy three-dimensional positioning with only two speakers, or a pair of headphones?
Congratulations, you’ve found that asterisk I said I was going to come back to!
Yay! Explain.
For headphones or any other two-channel system, Atmos positional data has to be down-mixed into two-channel audio. If you want to hear Atmos music with the highest fidelity to the recording, you’re going to need to play it over a system with at least four physical speakers. As far as I know, the only way to do that with Apple Music is to use an Apple TV box: it outputs Dolby Atmos over HDMI.
So it’s all a lie!
Well, not so fast. What Dolby Atmos does for Headphones is render binaural audio. Binaural audio is, per Wikipedia, “a method of recording sound that uses two microphones arranged with the intent to create a 3-D stereo sound sensation for the listener of actually being in the room with the performers or instruments.” Basically, the theory is that we only have two ears, yet we can clearly hear when sounds are up, down, front, or back, not just left or right. In theory, two channels should be enough to capture full positional information if we record the sound properly.
So: when there’s only two speakers to output to, the Atmos renderer takes each Atmos audio object and calculating volume and left/right panning settings to synthesize a binaural mix. All the positional information is still used.
Is it better stereo, or just different?
That’s hard to answer. First off, you may not hear much difference between binaural stereo and normal stereo. I hear what audio nerds call a “wider soundstage,” but I rarely think sounds are in front of me or behind me. Occasionally, I get that “enveloping sound” sensation they talk about, but I can also get that from a good normal stereo recording. In my experience, I’m more likely to get it from a pair of great full-range speakers than from headphones. From what I’ve read, I’m not an outlier here; the truth is that most people just don’t have great speakers.
That’s very audiophile snob of you.
Sorry.
You said “first off.” Second?
Second, the original multichannel Atmos mix just might not be as good, at least subjectively, as the stereo mix. Tracks are definitionally going to be placed differently, and you might find some are overemphasized or underemphasized to your tastes. This gets even more complicated if you’re listening to headphones, because you’re relying on the Atmos renderer to synthesize the binaural mix.
So is this an Apple exclusive thing? Apple talks about it like they’re doing amazing things nobody else has.
Apple talks about everything that way. Atmos Music has been a thing since at least 2017, and TIDAL and Amazon Music already stream it. When Apple says they’ve been working with studios on this, I have a suspicion that what they mean is “Dolby has been working with studios on this.” I haven’t seen any indication yet that Apple’s getting exclusive tracks and deals.
Huh. So what does any of this have to do with AirPods “Spatial Audio”?
Apple seems to be using that to describe two unrelated things:
- Their own clever synthesized binaural audio that they use with video playback, which only works between iOS and AirPods Pro and Max. This considers your physical position relative to the playback device when it’s calculating the binaural audio effects, making it seem like the “front center channel” is right where the video is playing regardless of your head’s position.
- Apple branding for Dolby Atmos music.
So does Spatial Audio work in Spatial Audio?
Come again?
Does the Dolby Atmos “Spatial Audio” music play back on AirPods Pro and Max using “Spatial Audio”?
Oh, gotcha! No.
Argh.
But, an Apple tech note says it’s coming “this fall,” which seems to mean “with iOS 15.” A friend with the developer beta says it’s already working in that release, and that when she turns her head she can sense the instruments “moving” on the soundstage. This suggests the Atmos binaural rendering is being reconfigured on the fly by dynamic head positioning.
If (Atmos) Spatial Audio isn’t (Apple) Spatial Audio, can I listen on non-Apple headphones and speakers?
Yes. If you’re using an Apple TV box, then It Just Works™. Otherwise, you’ll need to go into the Music app’s settings and set Atmos to “Always On” rather than “Automatic.” Apple Music warns that isn’t “supported” on all speakers, but I would read that as a warning that it may not sound good on all external speakers—remember, the Atmos binaural rendering happens in Apple Music itself. It should be fine on any decent headphones, though.
So is this really the future of music?
If anyone can finally make multichannel audio mainstream, it’s Apple, but that’s a big if—the consumer audio market has been rejecting multichannel audio for going on five decades. We’re going to have to wait a few years to see if “3-D music” really takes off, or if it goes the way of 3-D movies.
