Dolby MAT

What is Dolby MAT?

Dolby MAT stands for Metadata-enhanced Audio Transmission. It functions as an encode/conversion/transport/conversion/decode process rather than a codec or audio format itself. A MAT encoder (typically in source devices like Blu-ray players or streaming devices) packages variable bit-rate audio streams into encapsulated MAT frames, converts them to LPCM, and transmits them over HDMI at a fixed bit rate. A compatible receiver's MAT decoder then unpacks these frames back to their original bitstreams for processing.

MAT Versions and Supported Formats

Two versions of MAT exist. Dolby MAT 1.0 was designed to work with Dolby TrueHD, enabling lossless audio transport over HDMI. When Dolby Atmos was introduced, the technology was expanded to MAT 2.0, which supports encoding and decoding of Dolby Atmos metadata in real time by source devices, with object-based audio information dynamically encoded to limit latency and reduce processing complexity.

Dolby MAT facilitates three primary codec families: Dolby Digital Plus with Joint Object Coding (DD+ JOC, used by streaming sources), Dolby TrueHD (used by Blu-ray and UHD Blu-ray), and Dolby AC-4 (used by ATSC 3.0 broadcasting).

HDMI Bandwidth and eARC Requirements

HDMI 1.3 or later is required for Dolby MAT operation. The technology leverages HDMI's multi-channel audio lanes and aggregates their bandwidth to deliver high bit-rate streams. However, the practical distinction lies in ARC versus eARC:

Standard ARC carries approximately 1 Mbps of compressed audio, supporting only lossy Dolby Atmos via Dolby Digital Plus (DD+ JOC). eARC carries 37 Mbps, a 37-fold increase that enables lossless audio formats. eARC requires an Ultra High Speed HDMI cable certified for 48 Gbps; standard High Speed or Premium High Speed cables will silently downgrade the connection to ARC without warning.

eARC support is a device and firmware capability, not a mandatory feature tied exclusively to HDMI 2.1. While most HDMI 2.1-labeled ports include eARC, some HDMI 2.0 devices include eARC via firmware, and some HDMI 2.1 ports lack it. TVs built from 2018 and newer supporting eARC are generally designed to support Dolby Atmos passthrough, though compatibility varies by model.

Lossless Atmos: Real-World Sources

The availability of lossless Dolby Atmos depends on both the source material and the transport method. Lossless Dolby Atmos rides on Dolby TrueHD and requires eARC's full 37 Mbps bandwidth. The only source for lossless Dolby Atmos is UHD Blu-ray disc playback. Netflix, Disney+, HBO Max, Apple TV+, and other streaming services deliver lossy Atmos via Dolby Digital Plus with Joint Object Coding (DD+ JOC). Despite being lossy, this codec still carries full height-channel and object-based metadata and sounds indistinguishable from lossless on most compatible AVRs and soundbars. Lossy Dolby Atmos rides on top of Dolby Digital Plus and fits within ARC's bandwidth budget, making it accessible without eARC.

Common Compatibility and Configuration Issues

MAT passthrough failures typically stem from configuration rather than hardware incompatibility. Users must manually adjust settings including forcing passthrough audio, enabling eARC, and configuring HDMI to "enhanced" mode. These settings are often restricted by default on many TVs.

Devices may flag stereo content as Atmos, which disables surround enhancement processing in receivers, resulting in distinctly unimpressive audio despite quality equipment investment. Audio artifacts can occur if corrupt data is not filtered out of the PCM stream; Sonos Arc and Beam soundbars experienced a "pop of death" audio problem (loud, disruptive sounds) that was addressed in a November 2023 software update.

Some source devices output Dolby Atmos in MAT-wrapped format, which many modern AV receivers can decode, but compatibility with older TVs may be limited. When eARC is unavailable, users are limited to compressed (lossy) Atmos only.