- Dolby AC-4 was the popular codec of a number of audio execs
- Higher than current Atmos audio with out excessive bandwidth necessities
- Peacock is upgrading however different streamers have not introduced any plans
One of many largest variations between streamed films and 4K Blu-ray is the sound high quality: even the costliest streaming tiers ship compressed audio with a transparent discount in dynamic vary and readability in comparison with disc-based playback.
However that may change because of a brand new model of Dolby’s sound know-how that audio specialists apparently cannot inform aside from uncompressed PCM, however that works at streaming bitrates.
The brand new know-how known as Dolby AC-4, and it is a codec: an encoder/decoder for compressing audio. It is designed to ship a lot larger audio high quality than present streaming soundtracks, and might achieve this with out requiring a number of bandwidth.
With a little bit of assist from the New York part of the Audio Engineering Society and Engine Room Audio, the audio execs at Immersive Machines in the US set up a double-blind listening test the place audio specialists heard mixes in a number of codecs together with the present streaming customary, DD+JOC (utilizing the Dolby Digital+ codec).
Many times the specialists picked AC-4 as having the perfect sound high quality of the compressed audio codecs.
How Dolby AC-4 may make your streams sound sweeter
Most streaming apps use DD+JOC for immersive audio. It is a model of the tried and examined Dolby Digital customary, with the JOC bit standing for “Joint Object Coding”. It permits Dolby Atmos to ship positional audio with out breaking assist for five.1-channel setups.
Dolby AC-4 is what Dolby calls a Subsequent Era Audio codec, and it is designed to extra effectively ship audio for headphone and speaker listening, together with 3D object info.
As Dolby explains: “The AC-4 coding system makes use of new facets of object audio past what’s already obtainable with Dolby Atmos in different Dolby codecs for options like dialogue enhancement or commentator substitution.” And considerably, it “can ship equal channel-based audio high quality at roughly half the bitrate of Dolby Digital Plus”.
That is spectacular, however does it ship?
Immersive Machines’ listening check used three codecs: 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 identical system with particular audio system muted, and to particular person audio system soloed. Every format was given the letter A, B or C and their identities weren’t revealed till the check was completed.
The check wasn’t simply based mostly on vibes. Listeners had been requested to establish compression artefacts comparable to gating, “swishing”, lack of spatial precision and lack of frequency vary. And with all of the audio system on — ie, the way in which you’d hear at residence — AC-4 was in a useless warmth with the reference uncompressed PCM audio.
Compression was extra noticeable in AC4 when particular person audio system had been soloed, however for a full residence theater setup, AC-4 delivered sound that apparently matches lossless however whereas streaming simply 3% of the information.
There are some caveats right here, notably the pattern measurement: a check with 16 listeners is not arduous science. However on the identical time, 16 audio execs informed to hear critically are going to be way more choosy than you or I are more likely to be, so it is nonetheless fairly the endorsement.
The primary TV/film streaming service delivering AC-4 might be Peacock, though the know-how can also be being utilized by Amazon Music and TIDAL (however particularly for binaural headphones-based spatial audio). Different streamers might migrate however up to now there have not been extra bulletins since Peacock’s information at CES 2026.
Yow will discover out extra concerning the Immersive Machines testing here, however whereas it does counsel that streamers may ship related sound high quality to 4K Blu-ray within the very close to future, it is price noting that Dolby AC-4 would not handle one of many different causes folks purchase Blu-Ray discs: in contrast to streaming, purchased Blu-Rays do not disappear out of your library when streaming rights expire or the streamer decides to slim down its catalog.
Higher high quality has completely been a serious driver for why folks purchase 4K Blu-rays, particularly you probably have a terrific residence theater setup — however assortment and possession is rising as a motive why persons are changing into invested in Blu-ray once more, and AC4 will not change that.
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