- Dolby AC-4 was the codec of choice for several audio professionals
- Better than existing Atmos sound without high bandwidth requirements
- Peacock is upgrading, but other streamers have not announced any plans
One of the biggest differences between streamed movies and 4K Blu-ray is 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 could change thanks to a new version of Dolby’s audio technology, which audio experts apparently can’t tell apart from uncompressed PCM, but which works at streaming bitrates.
The new technology is called Dolby AC-4, and it’s a codec: an encoder/decoder to compress audio. It is designed to deliver much higher sound quality than current streaming soundtracks, and can do so without requiring a lot of bandwidth.
With a little help from the New York section of the Audio Engineering Society and Engine Room Audio, audio professionals 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 chose 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 is a version of the proven Dolby Digital standard, where the JOC bit stands for “Joint Object Coding”. It allows Dolby Atmos to deliver positional sound 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 exploits new aspects of object audio beyond what is already available with Dolby Atmos in other Dolby codecs for features such as dialogue enhancement or commentator replacement.” And significantly, it “can deliver equivalent channel-based sound quality at about half the bit rate of Dolby Digital Plus”.
It’s impressive, but does it deliver?
Immersive Machines’ listening tests used three formats: DD+JOC at 768 kbps, uncompressed PCM audio at 13,824 kbps, and AC-4 L4 at 448 kbps. Listeners heard them on a full 7.1.4-channel system, on the same system with specific speakers muted, and for individual speakers solo. Each format was given the letter A, B, or C, and their identities were not revealed until the test was completed.
The test wasn’t just based on vibes. Listeners were asked to identify compression artifacts such as gating, “swihing,” loss of spatial precision, and loss of frequency range. And with all the speakers on – ie. as you would listen at home – AC-4 was in dead heat with the reference uncompressed PCM audio.
Compression was more noticeable in the AC4 when soloing individual speakers, but for a full home theater setup, the AC-4 delivered sound that seemingly matches lossless, but while streaming only 3% of the data.
There are some caveats here, especially the sample size: a test with 16 listeners is not hard science. But at the same time, 16 audio pros asked to listen critically are going to be a lot more discerning than you or I probably are, so it’s still an endorsement.
The first TV/movie streaming service to provide AC-4 will be Peacock, although the technology is also used by Amazon Music and TIDAL (but specifically for binaural headphone-based spatial audio). Other streamers may migrate, but so far there have been no further announcements since Peacock’s news at CES 2026.
You can find out more about the Immersive Machines testing here, but while it suggests 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, purchased Blu-rays don’t disappear from your library’s slim stream or when its slim stream’s catalog goes down.
Better quality has definitely been a major driver of why people buy 4K Blu-rays, especially if you have a great home theater setup – but collecting and ownership is growing as a reason people are reinvesting in Blu-ray, and AC4 won’t change that.
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