Dolby Atmos | What Is It?

An audio format that allows the formation and delivery of audio above and beyond the usual stereo, Dolby Atmos immerses the audience in an authentic 3D audio experience.

When listening to music in stereo, we only perceive sound coming from either the left or right speaker. With the introduction of surround, we were also able to feel sound coming from behind us. What Dolby Atmos has brought to the table now is the possibility to position elements in the sound field in a 3D space, enabling us to create the illusion of sound coming from any direction around the audience, thus enhancing the clarity, depth and fidelity of the audio.

A typical surround sound system consists of left, centre, right and surround speakers, divided acoustically into two or four zones. All speakers within a zone receive the same audio information.

In a Dolby Atmos setup, these zones are enhanced and expanded thanks to the addition of overhead and extra surround speakers. In addition, all speakers in the Atmos setup are powered independently and receive their own audio feed which makes them their own acoustic zone.

To mix in Dolby Atmos, an array of front, back, side, and overhead speakers are required. The minimum setup is a 7.1.4 speaker array: 3 at the front, 2 at the sides, 2 at the back, 4 overheads and 1 Low-Frequency Effects subwoofer (LFE).

Atmos is an object-based format. This means that audio sources are considered objects in the sound field that can be located within the immersive space.

There are two key elements in an Atmos mix: Beds and Objects.

Beds are single or groups of audio channels that send audio to speaker locations. You can consider them as your foundation of the 3D space we are creating. Sounds like ambient effects or music backgrounds benefit from being placed in these beds.

On the other hand, Objects are sounds that can be moved freely around the 3-dimensional space. This allows filmmakers to decide exactly where the sound should come from and where it should move. From a helicopter flying above the audience, or a car passing by to your left-hand side.

Dolby Atmos allows running up to 128 audio tracks divided in 10 beds (along 9.1 channels/speakers) and up to 118 audio objects. There are different approaches when mixing all these elements and it is very dependent on the material being mixed, but most of the sound field in a movie can be achieved using Beds correctly and applying some of the workflow when mixing in traditional surround. It is very exciting to be able to place sounds in a 3D environment to enhance the experience of the listener but it is important to remember what is the end goal. The sound needs to help deliver the main message of the production without being too distracting. Keeping the mix in a place where people can understand it.

But, it is not only about the speakers. The Atmos processing plays a big part in the system as it is able to assign each audio track to its corresponding speaker within the room regardless of its size. It doesn’t matter if you experience the playback in a 64 speaker theatre, with smart speakers, soundbars or mobiles, the Atmos processor will be able to adapt to each system and produce the same effect.

The software behind the creation of these translatable mixes is the Atmos Renderer. This software creates a master Atmos format audio file that contains all the mix information, including 128 channels of audio, panning metadata and binaural settings. In short, one mix to rule them all. A single file that can be played on all the Atmos-enabled systems and devices in the market and that can be delivered together with the other mixing formats.