Dolby Atmos

In the field of audio reproduction, Dolby Atmos has definitely come by as the next big thing. Professionals and the people who have tried out Dolby Atmos invariably describe it as the most immersive audio experience they have come across in their lives. It seems as though the sound is moving around you in a 360-degree hemisphere.

So, when one has had the experience of sitting in a room equipped with Atmos, one can, but, be impressed. A quick glance at the history of audio standards shows that despite the best efforts put in, few things have worked. People prefer to listen to their music over earphones, headphones or a pair of speakers.

The factor that makes Atmos stand out in a sea of changes is object-based mixing. It’s an enhancement over the channel-based mixing that earlier used to be in prominence. The ramifications of object-based mixing reach far and wide.

Another factor that stands in the favor of Atmos is that it is favoured by Apple, which implements Atmos for the Apple Music streaming platform.

Object-Based Mixing

In the case of Channel-Based Mixing or CBM, one takes a number of stereo and mono tracks and sums them together for creating a stereo mix file, while using a conventional stereo bounce. But an important problem arises when this methodology is put to avail. As the mix is locked into place, one is forever left with two interleaved files.

When we turn our focus towards, Object Based Mixing (OBM), we see that your sources are going to remain discreet. They do not merge into fixed out files. Instead, it is as individual objects that they are encoded. They are further assigned a position within the 3D space.

Now, with this space being virtual and featuring a fixed shape, the position of the element also becomes easy to apply. It may be applied to several places, ranging from a small home entertainment room, to a cinema hall, on to a stadium. One may alternately use the system for stereo playback.

Objects and Beds

In a mix, any single discreet element is referred to as an object. So, a few of the examples of objects, here, are vocals, guitar, and kick drum. It would, hence, be right to perceive objects as Atmos’ equivalent for channels. It is, further, possible to move about objects freely across a 3d space. One could automate the size, height, and position.

Now, within an array, when sources are sent to specific channels, a bed is used for the purpose. Just as an instance, when you conduct a stereo recording for a piano, you may choose to send two sources merely to the left and the right channels.

So, you may choose to have beds that output in any number of configurations within the mix. This may include standards such as 5.1 and 7.1. This, further, becomes utilitarian from the processing perspective as well, because one can now treat the bed as a single part.

Minimum system requirements for Atmos

• An interface that can output 12 channels with ganged level control for each channel
• 12 speakers: Left, Right, Center, Left Surround, Left Rear Surround, Right Surround, Right Rear Surround, plus 4 height channels that are mounted above the listener and are arranged in a square with the mix position in the centre.
• A methodology that time aligns all these speakers. While it is possible, the speakers should be calibrated for the best possible output in full range.
• A filter matrix on the outputs wherein the Dolby Curve can be applied.

Let us now consider an example of a configuration which will be ideally suited for a small-sized room.

• Avid HD Native Thunderbolt
• 3x Neumann KH310 (LCR)
• Avid MTRX Studio
• 4x Neumann KH120 (Ls, Rs, Lrs, Rrs)
• 2x Neumann KH750 (LFE, clustered)
• 4x Neumann KH80 (Ltf, Rtf, Ltr, Rtr)

Applying the Dolby Curve

It’s now the time to apply the Dolby curve to the system. But before that, it becomes important to ensure that while the speakers are bolted to the ceiling and walls, they are time-calibrated and aligned as well.

We apply the Dolby curve such that among all Atmos applications, there is a common reference point.

Now, RT60 is a measurement of the time taken by the loudest noise in a concert hall to fade to the background level. When we consider RT60 of a small room, it is going to be much longer than that of a large treated theatre. So, the additional build-up of bass skews the mix.

The curve pulls out a carefully calculated amount of the low end. This brings the perceived low-end output of a small space in line with a full theatrical playback system.

Apple and Atmos

Let us now take a look at an interesting story that concerns Apple and Atmos. One of the most important factors that led to the adoption of Dolby Digital Plus JOC was Apple’s announcement concerning the revised delivery specification for their streaming platform. In case a Mix engineer wanted to get on Apple Music, he was required to deliver an Object Based Mix.

Then, suddenly, Apple came up with an iPhone update. Herein, in the settings, they added the Spatial Audio tickbox and further enabled it by default.

But, typically, this rendered the implication that numerous consumers who used Airpods had begun to listen to Atmos even without knowing it. This way, the iPhone users using Airpods became the single largest demographic for consuming 3d audio. They were thousand-folds more than the other people who were listening to Atmos.

This, nevertheless, gave rise to an issue as well. For their Spatial Audio, Apple used the older AC-4 format. But, Dolby in their Renderers and RMUs use DD+ JOC. This is a matter to be looked into, because the two don’t fold to binaural in the same way.

So, when you mix a track through Dolby monitoring system, and have it folded down to Binaural for a headphone mix check, it won’t sound the same as it does on iPhone.

The only way to get an idea of how your mix sounds on Airpods with an iPhone, is to bounce the file as an MP4 and then play it back on an iPhone — not exactly slick. At time of publication, there is no way to monitor your mix as it would sound on iPhone in real time.