The audio capabilities of Blu-ray are among its most significant and least discussed advantages over other home cinema source formats. While much attention is paid to resolution and HDR in discussions of picture quality, the audio codecs carried on Blu-ray discs represent a genuinely transformative step from the lossy audio that preceded and surrounds them.
Two lossless audio codecs are used on Blu-ray: Dolby TrueHD and DTS-HD Master Audio. Both achieve lossless compression — the decoded audio is bit-for-bit identical to the studio master from which it was encoded. This is the same mathematical standard applied to lossless music files in the two-channel audio world: no information is discarded, no approximation is made, and the output at decoding is guaranteed to match the input at encoding.
Dolby TrueHD is the lossless codec used for Dolby Atmos content on Blu-ray. It carries the full object-based Atmos audio mix — including the height channels that define Atmos’s dimensional sound presentation — in a lossless container. DTS-HD Master Audio carries the lossless version of DTS-X and conventional DTS surround mixes. Both support channel counts from stereo to 7.1 and beyond, and both are decoded by the disc player itself or passed as a bitstream to a capable AV receiver or processor for decoding.
The comparison with streaming audio is concrete and audible. A Blu-ray disc carrying a Dolby TrueHD 7.1 mix at a bitrate of 5 to 8 Mbps delivers the studio master. A streaming version of the same film carrying Dolby Digital Plus at 640 to 768 kbps has been compressed by a factor of ten or more. Streaming services have made significant improvements to their audio quality in recent years, and at their highest tiers they deliver a satisfying result. But a direct comparison between the lossless disc and the compressed stream on a capable system consistently reveals the disc’s advantage in textural resolution, dynamic accuracy, and spatial precision.
Lossless audio is not an audiophile abstraction. On a well-designed home cinema system, it is audibly different from its compressed alternative — and the difference is in favour of what the filmmakers intended.