- Dolby AC-4 was the preferred codec of multiple audio pros
- Better than existing Atmos audio without high bandwidth requirements
- Peacock is upgrading but other streamers haven’t announced any plans
One of the biggest differences between streamed movies and 4K Blu-ray is the sound quality: even the most expensive streaming tiers deliver compressed audio with a clear reduction in dynamic range and clarity compared to disc-based playback.
But that might change thanks to a new version of Dolby’s sound technology that audio experts apparently can’t tell apart from uncompressed PCM, but that works at streaming bitrates.
The new technology is called Dolby AC-4, and it’s a codec: an encoder/decoder for compressing audio. It’s designed to deliver much higher audio quality than current streaming soundtracks, and can do so without requiring lots of bandwidth.
With a bit of help from the New York section of the Audio Engineering Society and Engine Room Audio, the audio pros at Immersive Machines in the US set up a double-blind listening test where audio experts heard mixes in multiple formats including the current streaming standard, DD+JOC (using the Dolby Digital+ codec).
Again and again the experts picked AC-4 as having the best sound quality of the compressed audio formats.
How Dolby AC-4 could make your streams sound sweeter
Most streaming apps use DD+JOC for immersive audio. It’s a version of the tried and tested Dolby Digital standard, with the JOC bit standing for “Joint Object Coding”. It enables Dolby Atmos to deliver positional audio without breaking support for 5.1-channel setups.
Dolby AC-4 is what Dolby calls a Next Generation Audio codec, and it’s designed to more efficiently deliver audio for headphone and speaker listening, including 3D object information.
As Dolby explains: “The AC-4 coding system utilizes new aspects of object audio beyond what is already available with Dolby Atmos in other Dolby codecs for features like dialogue enhancement or commentator substitution.” And significantly, it “can deliver equivalent channel-based audio quality at roughly half the bitrate of Dolby Digital Plus”.
That’s impressive, but does it deliver?
Immersive Machines’ listening test used three formats: DD+JOC at 768 kbps, uncompressed PCM audio at 13,824 kbps, and AC-4 L4 at 448 kbps. The listeners heard them on a full 7.1.4-channel system, on the same system with specific speakers muted, and to individual speakers soloed. Each format was given the letter A, B or C and their identities weren’t revealed until the test was done.
The test wasn’t just based on vibes. Listeners were asked to identify compression artefacts such as gating, “swishing”, loss of spatial precision and loss of frequency range. And with all the speakers on — ie, the way you’d listen at home — AC-4 was in a dead heat with the reference uncompressed PCM audio.
Compression was more noticeable in AC4 when individual speakers were soloed, but for a full home theater setup, AC-4 delivered sound that apparently matches lossless but while streaming just 3% of the data.
There are some caveats here, notably the sample size: a test with 16 listeners isn’t hard science. But at the same time, 16 audio pros told to listen critically are going to be much more picky than you or I are likely to be, so it’s still quite the endorsement.
The first TV/movie streaming service delivering AC-4 will be Peacock, although the technology is also being used by Amazon Music and TIDAL (but specifically for binaural headphones-based spatial audio). Other streamers may migrate but so far there haven’t been more announcements since Peacock’s news at CES 2026.
You can find out more about the Immersive Machines testing here, but while it does suggest that streamers could deliver similar sound quality to 4K Blu-ray in the very near future, it’s worth noting that Dolby AC-4 doesn’t address one of the other reasons people buy Blu-Ray discs: unlike streaming, bought Blu-Rays don’t disappear from your library when streaming rights expire or the streamer decides to slim down its catalog.
Better quality has absolutely been a major driver for why people buy 4K Blu-rays, especially if you have a great home theater setup — but collection and ownership is growing as a reason why people are becoming invested in Blu-ray again, and AC4 won’t change that.
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