Dolby vs Multichannel PCM, AM I correct?


Novice Member

I have been doing some research and I wanted to run things by people who know much more than I do.

The basic setup, Apple TV 2021 (encoding), LG CX, and Sonos Beam 2 (decoding).

Apple TV set up to Audio Auto, LG CX set up to pass through, and Sonos Beam 2 is the thing that ought to do all the audio encoding.


It is my understanding that using pass-through on LG CX so that Sonos Beam 2 does the decoding is the only way I can get full uncompressed Atoms to my Sonos because it is the only way to Get Dolby TrueHD.

If LG CX is set to Auto under digital audio out the Sonos still encodes Atoms but it is somehow not the full experience because it lacks the Dolby TrueHD.

Am I correct on this?


And this one is the rabbit hole, or so I think. It has to do with Dolby Digital Plus 5.1 vs Multichannel PCM 5.1 and 7.1.

First things first, the Apple TV product page says that Apple TV only supports Dolby Digital Plus 7.1. On the 5.1 it says it supports Dolby Digital 5.1 and not the plus.

Now, in the config where TV does to pass-through to Sonos from Apple TV when I watch content that is Dolby Digital Plus 5.1 from say Netflix, I get on Sonos Multichannel PCM 7.1 and this is because of Apple TV’s inability to play Dolby Digital Plus 5.1. (the same content played via TV OS on LG CX gives me in Sonos proper Dolby Digital Plus 5.1).

If I change the digital audio out on my LG CX to auto and then try to pass the Dolby Digital Plus 5.1 audio from my Apple TV to Sonos what I get in Sonos is Dolby Multichannel PCM 5.1, which is something I could not find an answer to.

Right now, there is no content on streaming services that actually do Dolby Digital Plus 7.1 but if there was, using the Apple TV as the source and LG CX as pass-through, my Sonos would properly decode Dolby Digital Plus 7.1.

Whenever Sonos is displaying multichannel PCM it means it is not decoding the source audio properly, as in it is outputting something different to the source audio.

Multichannel PCM is better than Dolby because it is uncompressed and Dolby is based on multichannel PCM. This is a wired observation, I have been watching Dolby Digital Plus 5.1 content in Multichannel PCM 7.1 and the sound mix seems so much quieter, and also the sound mix such as voices seem to be placed behind everything else like they have been pushed behind other sounds.

And finally, right now there is no solution for Sonos to decode Dolby Digital Plus 5.1 when using Apple TV as a source.

Am I correct?

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