When mixing in Dolby Atmos, a combination of Beds and Objects is used to place sounds in three-dimensional space. Typically, Dolby Atmos music mixes will use one Bed and up to 118 Objects. In post-production workflows, multiple Beds are used to allow for separate re-renders of dialog, music and effects.

This article provides an overview of Beds and Objects, their advantages and limitations, and offers considerations for selecting the optimal approach for a project.

 

Beds:

A Bed is a multichannel mix bus with a fixed channel configuration. The default channel configuration of the Bed is 7.1.2 (Left, Center, Right, Left-Side-Surround, Right Side-Surround, Left Rear-Surround, Right Rear-Surround, LFE, Left-Top, Right-Top). The channels of the Bed have a fixed routing to specific loudspeaker locations. For example, Channel 1 of the Bed will always be routed to the Front Left loudspeaker, Channel 2 will always be routed to the Front Right loudspeaker and so on.

All Dolby Atmos compatible DAWs allow sending signals to the Bed, using the standard panner of the DAW. The workflow is basically the same as mixing traditional channel-based audio formats such as 5.1 or 7.1

 

Objects:

An object is a discrete audio element that can be placed anywhere in the three-dimensional sound field. Objects can consist of mono or stereo content and are positioned via dedicated Dolby Atmos panning metadata. Objects will always use all available loudspeakers of a Dolby Atmos setup and therefore offer the highest positional accuracy. With objects, any position in space can be addressed and the position will always be represented as precisely as possible. This also makes objects the best choice for any elements of the mix that are moving.

 

Considerations on when to use Beds and Objects

In most cases, using a combination Beds and Objects will yield the best results. The choice of using an object versus a bed for a specific element of the mix is entirely up to the mixer, however there are a few things to keep in mind:

 

• A Bed cannot address any locations in space outside of the 7.1.2 configuration. This means the with a Bed it is not possible to individually address the front and rear overhead speakers, or the wide speakers positioned between the front and side surrounds. For any audio elements where a precise placement along the ceiling or in the wide-surround speakers is desired, objects should be used.

 

• Any element of the mix that is placed in between the fixed speaker positions or that is moving dynamically through space benefits greatly from the panning accuracy of Objects. Using Objects for such signals also improves the spatial accuracy of the Dolby Atmos headphone rendering algorithm.

 

• Binaural metadata settings are applied to individual bed channels, but if there are multiple beds all instances of that channel will have the same binaural render mode. Individual Binaural Metadata can be set for each Object. Therefore, any element of the mix where a specific, individual Binaural Metadata setting is needed should be an Object.

 

• Beds can be very useful when the source material is already recorded in a multichannel format, for example live music recordings done with a multichannel microphone array, or multichannel field-recordings. Beds offer an easy way to route these types of signals in a Dolby Atmos mix.

 

• The Bed is also the easiest way to route the output of multichannel reverb plug-ins within a Dolby Atmos mix.

 

• The LFE channel can only be addressed via the Bed. Read more about how to use the LFE channel within a Dolby Atmos Mix here.

 

• Signals that stay static in a fixed location (such as dialog that is panned to the center channel for the duration of the program, or a music stem that is routed to L/R) don't benefit from the panning accuracy of Objects, and can therefore be sent either to a bed or an Object, whatever is easiest in a given mixing session.

 

An alternative approach is the Object bed, which uses static objects to mitigate some of the limitations of the bed. More information can be found here.