Audio Objects vs Bed Channels Audio Objects vs Bed Channels

How beds and objects work

A bed track is routed to a single multichannel surround bus, in formats up to 7.1.2, and behaves like a conventional channel-based mix. It is "a straight-up expansion on a stereo bus, adding extra channels but working in the same way." Once assigned to a bed, a signal is committed to specific speaker feeds, just as it would be in a standard 5.1 or 7.1 mix.

An object is handled differently. Rather than assigning a signal to specific speakers with a horizontal channel panner, a mix engineer places it using a three-dimensional panner interface, dragging an icon to the position in the sound field where the object should appear. That positional information is written into the object as metadata, which the playback system decodes in real time to adapt the spatial placement to whatever speaker array is actually deployed. DTS:X uses the same underlying concept. "An audio object is an audio element with associated metadata that defines how it is rendered in the listening environment." During cinema playback, each theater's Atmos system renders objects in real time based on the known locations of its loudspeakers, so an object is heard as originating from its designated coordinates regardless of the room's exact speaker positions.

Key specifics of Atmos and DTS:X

Each Dolby Atmos audio track can be assigned either to a conventional channel (a bed) or to an object. Dolby Atmos technology allows storage and distribution of up to 128 audio tracks, together with metadata describing properties such as position and volume and how they vary over time. In cinema, Dolby Atmos uses a 9.1 channel-based bed (7.1 surround plus 2 overhead channels) for ambience stems and center dialogue, leaving up to 118 of those tracks available for objects.

DTS:X Pro handles beds differently from consumer DTS:X. It upmixes bed channels using the Neural:X upmix engine to as many as 30 different speakers, rather than confining them to a fixed 7.1.2-style bus. In cinema DTS:X mixes, bed channels are played through 9 main channels for almost the entire runtime of a movie, with discrete high-spatial-resolution objects layered in alongside them.

Comparison to fixed 5.1/7.1

Conventional multichannel technology "burns all the source audio tracks into a fixed number of channels during post-production." The mix is locked to a specific channel count and speaker arrangement at the time it is finished. Object-based rendering breaks that link: an object can be manipulated in space, encoded into a DTS or Dolby bitstream, and then recreated accurately in a listener's home using whatever specific speaker setup that listener has, rather than being confined to a specific channel such as a discrete left speaker. Because the spatial metadata is decoded at playback rather than baked into fixed channels, an Atmos mix automatically optimizes itself to work as well as possible on any Atmos-capable setup, whether that is a 5.1.2 soundbar or a 9.1.6 dedicated room.

Common confusions

A bed is not a separate mixing concept from ordinary channel-based audio. It behaves exactly like a normal stereo or surround channel bus, just with additional channels added on top. Beds are rendered as a static, fixed-position signal: unlike objects, they are not remapped or upmixed dynamically based on the specific playback speaker array, except where a codec extension explicitly adds that capability, as DTS:X Pro does with its Neural:X-based bed upmixing to up to 30 speakers.