Dolby Atmos codecs on Sonos Arc

I’ve been searching for this specific thread and I’m grateful to find it.

I have the same question plus another related one: I also have the LG CX and when I set audio settings Digital Sound Out to “Auto” on the HDMI input connected to my Apple TV, I get Dolby Atmos detected on the Sonos app.

This is the rub, though. I have the eArc setting on this HDMI input set to “On.” It’s also on for the actual eArc HDMI input. So it’s effectively on twice (I think).

If I turn the eArc to “Off” on the HDMI input connected to the Apple TV and set it to pass through, I get Dolby Atmos (DD +) on the Sonos app. If I attempt passthrough with the eArc mode on the HDMI connected to the Apple TV to “On,” it reverses all the existing picture settings such as motion smoothing, which turns on for some reason even though it’s an audio setting.

A bit confusing, I realize. I’ve been confounded by this for two weeks.

But based on what I’m reading above, for Apple TV streaming content, it should be displayed as Dolby Atmos DD +. Ergo, the eArc should be turned off the for input connected to the Apple TV and only the actual eArc HDMI port should be set to “On.”

Any advice or confirmation on this would be greatly appreciated.

@DonF What specific content are you testing on the Apple TV? When playing non-Atmos content, does it display the correct audio format in the Sonos app with either setting?

FYI, the Apple TV 4K uses Dolby MAT to play Dolby Atmos content which is a form of PCM audio. So I don’t think the Apple TV should be outputting any Dolby Atmos audio via Dolby Digital Plus. When I play Dolby Atmos content from my Apple TV, it only says “Dolby Atmos” on the Sonos app, not “Dolby Atmos (DD+)”.

@GuitarSuperstar I’ve been playing mostly Atmos content via apps, but any other format is appearing properly in the Sonos app when the TV audio setting is set to “Auto.” I was testing a Netflix program earlier via ATV4K and it displayed as Dolby Digital 5.1 PCM. So it’s not just outputting all content as Atmos.

I continued to deep dive after posting and, while most recommendations are to set the TV audio at passthrough, “Auto” is the only one that appears to work properly for me. I’ve tried every permutation and passing through audio on the TV from the ATV4K not only loses the full Atmos label, it won’t display Dolby Vision in this state. Which makes no sense, but the TV goes black momentarily, refreshes and the Dolby Vision label will no longer appear when audio “passthrough” is selected..

Needless to say I prefer both of these to be active.

I thank you for the feedback. This has been quite a puzzle to solve.

Watching a movie on Amazon with auto shows Dolby multichannel pcm 5.1, pass through as Dolby digital plus 5.1.  

@Ggnore Dolby Digital Plus is what you want to be getting from Prime Video.