Dolby is a well-known company in the cinema and home theater space, involved in the design of cutting edge technologies used on both the video and audio side of professional and consumer equipment. The company has gradually been extending its expertise to mobile with the adoption of HDR display specifications, and has its Dolby Atmos audio technology inside a few handsets too.

Although by no means universally adopted, Dolby Atmos is available in a growing number of handsets across price points. The technology also appears to be coming to Samsung’s Galaxy S8 and S8 Plus flagships via a future software update. 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 audio technology. It expands on the more familiar 5.1 and 7.1 surround sound formats. Amtos differs by providing not only surround sound in the x and y axes, but also in the 3D plane z axis, with the introduction of variable height for sounds. Its take on channel encoding doesn’t pre-mix audio for a specific setup, instead it takes an object-based approach to saving audio data which is mixed together 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 home and commercial theatres to install speakers in the ceiling for an additional height variable. It also increases the maximum number of supported speakers in a system up to 64. Although in the home Dolby recommends just adding two or four reflective or ceiling installed speakers to your existing 5.1 or 7.1 setup, it supports up to 34 speakers in total.

In cinemas, the Dolby Atmos format 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-setup agnostic.

Dolby

In the home theater and mobile versions, 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 the 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 at the AV receiver or on your smartphone’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 support on the content side. The format requires content to be specifically mastered for it, so it’s far from universal. Fortunately hundreds of Hollywood blockbusters have been produced in Atmos, going all the way back to 2012. The format is supported on regular and Ultra HD Blu-ray discs, and streaming services Hulu Plus, VUDU, 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 back content over headphones. The mobile version aims to emulate the 3D audio effect you get with a typical surround-sound system.

3D Sound Labs Manipulating a range of frequency and time based audio cues is the key to simulating surround sound through headphones.

How Dolby does it

This isn’t a new 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 if you were 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 would take 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 would also have to travel through your skull, acting as a filter for higher frequencies. The shape of your outer ear (pinna) also 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 invisible cues. By modeling these phenomena in software for playback over headphones, 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 takes how multiple sound sources interact with each other in space before they reach our ears into consideration. Subtle reflections and echo can help inform us about the distance of a source and the size and texture of a space. Multiple sounds will undergo phase cancellation when they meet in space, quieter sounds may be masked by louder ones, and high frequencies 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 very widely supported yet, but additional adoption is likely. According to Dolby’s website, just four smartphones currently support Dolby Atmos technology. A leaked update suggests support for the Samsung Galaxy S8 and S8 Plus is on the way too, and Samsung might also include the feature out of the box in its next-generation flagships.

Here’s the full list of supported devices according to Dolby’s website. Keep in mind that there may be a few others out there that aren’t listed:

Atmos isn’t the only Dolby audio technology you can find in smartphones though. A number of handsets also boast the company’s Digital Plus 5.1 surround-sound setup and other audio technologies too. Digital Plus technology is based on very similar psychoacoustic perception models for spatial audio, but doesn’t support Atmos’ new z-axis height feature. The Razer Phone is the first phone to support both HDR and Dolby Digital Plus content from Netflix. Other phones sporting Dolby Audio in some form include a number of ZTE smartphones, the LG G6, and any HTC phone featuring BoomSound. There are probably a few more out there, but documentation of these features is pretty inconsistent.

If you’re big on watching movies on your phone, hunting down one of the few handsets with Atmos support might be worth the effort, provided you can stream compatible content. Remember, this technology only benefits film and TV. A smartphone with Dolby Atmos technology could be the perfect companion to your high-end home cinema system when on the move. Hopefully we’ll see more smartphones sporting the technology throughout 2018.