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What you need to know about Dolby Atmos sound
Dolby is a well-known company in the cinema and home theater space, involved in the design of cutting-edge audio and video technologies for professional and consumer equipment. The company has gradually been extending its expertise to mobile, with the adoption of HDR display specifications, and support for Dolby Atmos surround sound inside many phones.
Atmos is available in a growing number of devices across different price points, ranging from budget phones like the Samsung Galaxy F62 through to expensive flagships like the Galaxy Z Fold 3. If you’re wondering what all the fuss is about, then you’re in the right place.
What Dolby Atmos does
Atmos is Dolby’s latest surround-sound technology, expanding on its traditional 5.1- and 7.1-channel formats. Atmos differs by focusing not just on the X and Y axes, but also on the vertical Z plane. Its take on channel encoding doesn’t pre-mix audio for a specific setup — instead, it uses an object-based approach, which is mixed right before the sound comes out of your speakers. Dolby calls Atmos “the most significant development in cinema audio since surround-sound.”
Atmos introduces a new height variable to traditional surround sound and changes the way Dolby encodes audio channels.
Atmos was primarily designed for cinema and high-end home installations, enabling the additional height variable through ceiling speakers. It also increases the maximum number of speakers in those systems to 64. In the home Dolby recommends adding just two or four reflective or ceiling-installed speakers to an existing 5.1 or 7.1 setup, but you can use up to 34 speakers if you’re rolling in cash.
Back in cinemas, Dolby Atmos allows for up to 128 tracks and audio objects, complete with spatial metadata, mixed in-house on powerful hardware to match the specific cinema speaker setup, ensuring highly accurate sound placement. In other words, the format is speaker agnostic.
In home theater or mobile incarnations, audio is encoded alongside spatial information into Dolby TrueHD or Digital Plus formats. These formats traditionally support up to 15 or 16 audio channels, but Dolby is using a new encoding method that doesn’t split data into pre-mixed channels. Instead, it’s a spatially-encoded digital signal with panning metadata. This audio is then mixed together for any Atmos surround-sound setup in your home via an AV receiver or another device’s processor, while still reproducing the sound accuracy you would hear in the cinema.
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The final piece of the puzzle is content compatibility. The format requires content to be specifically mastered for it, so it’s far from the default. Fortunately, hundreds of Hollywood blockbusters have been produced in Atmos, going all the way back to 2012. The format is supported on Blu-ray discs, and streaming services like HBO Max and Netflix also offer some Atmos titles.
Of course, smartphones don’t have access to multiple speaker placements. You’re lucky if your phone has two front-facing speakers. Instead Dolby Atmos for smartphones is a software-based solution that kicks in when playing content over headphones. The mobile version aims to emulate the 3D audio effect you get with a typical surround-sound system.
How Dolby does it
This isn’t an original idea. 3D spatial modeling for stereo headphones has been around of a while now. It’s based on a number of acoustic cues and heat-related transfer functions, which essentially reverse-engineer the way human hearing works to recreate sounds in what seems like a 3D space.
Consider what happens when you sit in the middle of a surround-sound system. Better yet, imagine yourself actually sitting in the middle of a film scene. When a sound leaves a particular source, say an explosion, it takes time to reach our ears. If the sound is on one side of you, the same sound takes a little bit longer to reach your other ear, meaning there’s a slight time or phase difference between your ears, which your brain detects. The sound also has to travel through your skull, acting as a filter for higher frequencies. The shape of your outer ear (pinna) acts as a resonance filter, helping your brain determine the direction and height of sounds around you.
In smartphones, Dolby Atmos is a software technology that mixes and filters multi-channel audio for your stereo headphones. It retains a 3D -sounding experience by using binaural audio techniques.
Subconsciously, your brain is incredibly adept at picking up on these cues. By modeling these phenomena in software for headphone playback, it’s possible to trick your brain into believing sounds are coming from any direction, even when the speakers (headphones) are right next to your ears. For proof, check out one of the myriad impressive binaural audio clips available on YouTube.
A top-notch surround-sound emulator also accounts for how multiple sound sources interact with each other before they reach our ears. Subtle reflections and echo can inform us about the distance of a source, as well as the size and texture of a space. Multiple sounds will undergo phase cancellation when they meet, quieter sounds may be masked by louder ones, and high frequencies can become dampened over longer distances. All of this has to be calculated and mixed down from a 5.1, 7.1, or Atmos format into a stereo signal.
Which phones support it?
Dolby Atmos isn’t universally supported yet, but that future isn’t far off. In fact if you’re buying a new flagship phone from companies like Apple, Motorola, Oppo, or Samsung, you can practically guarantee it. As mentioned before, it’s already on a lot of budget and mid-range phones too. Two conspicuous gaps are the Google Pixel 6 and 6 Pro. Sadly, there’s no sign that they’ll get it anytime soon.
Atmos isn’t the only high-end Dolby audio technology you can find in smartphones. A number of devices boast the company’s Digital Plus format, which is based on similar psychoacoustic perception models for spatial audio.
Hunting down a phone with Atmos support is probably worth the effort, provided you can stream compatible content. You’ll need to check the services you use, and even then, not everything you watch or listen to will be labeled for it. Many older movies and TV shows are never going to get an Atmos mix, and the format is even rarer when it comes to music. There are compatible tracks on services like Tidal and Apple Music. We may see more widespread adoption once Spotify launches its HiFi tier, but we’ll have to wait and see on that front.