Dolby Atmos has been an innovative way to deliver music and movies to the public ever since its launch in 2012. Studios and cinemas around the world have included this technology into their workflow to produce immersive audio experiences.
Streaming services such as Netflix and Amazon have even started asking for content to be delivered in this format.
Here, we will uncover exactly what Dolby Atmos is and how it works.
WHAT IS DOLBY ATMOS?
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.
THE SETUP FOR DOLBY ATMOS
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).
BEDS & OBJECTS
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.
MIXING IN DOLBY ATMOS
The Renderer also allows monitoring the projects in different formats and speaker setups. This way the mixes can be taken across different studios with different speaker counts and still monitor everything as expected.
The sound needs to help deliver the main message of the production without being too distracting.
An engineer's workflow when mixing in Atmos starts by monitoring in stereo whilst undertaking all the panning and object placing for 7.1.4. Based on their experience and understanding of how the system will perform for different materials, they will be able to make decisions on which elements and how much signal to send to each speaker. They will then finalise the mix in the studio with the full-size Atmos rig to tweak the small details and make sure the mix is at its best.
If the engineer is working as a mixer and not in an editorial capacity, they may try and work in Atmos from start to finish where possible. When working as an editor, they may work in stereo knowing that the mixer will be making a call on those choices in a fully Atmos capable studio afterwards during the final mix.
But Atmos can also be experienced using binaural rendering to allow monitor immersive mixes on headphones. Binaural is a two-channel audio intended to be played directly into the ears of the listener. It allows them to experience sound all around them as they do in the natural world.
Having the possibility of starting Atmos mixes using only a pair of headphones and at the same time experiencing how the mixes will translate in user devices can be of great help for engineers.
Long gone is the time when Atmos was only meant for big theatres and blockbuster movies. More and more distributors, manufacturers and creators are incorporating Atmos in their services and productions.