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Configuration: Apple TV (ATV) 4K → LG C9 oled eARC→ Sonos Arc

In the ATV Atmos is switched on, LG is set to passthrough, bitstream

 

When I play an Atmos movie from the Netflix app in the ATV I get Atmos from the Sonos ARC with the Atmos logo showing in the Sonos app.

When I play an Atmos enabled movie from the Apple movies app the sound is marked as Stereo 2.0 in the Sonos app and some audio channels seem to me missing in action as all e.g. speech is missing and only some surround is heard.

Turning off Atmos support (but not changing the export format) in the ATV does not help. Only when I force the output in the ATV to DD 5.1 I get 5.1 surround from the Sonos Arc. 

 

Is this happening because the Atmos sound is differently embedded in the Apple movies compared to the Netflix movies?
Is there a solution? Who should I blame? Apple movie because of their Atmos coding or the Sonos Arc because it does not support the Apple movies Atmos format?

(off topic but just to ventilate my frustration: why can’t, even in 2020, three high end devices not just simply work together...)

 

 

This is likely because your C9 has been updated to the latest firmware which allows multi channel LPCM pass through from devices like the Apple TV  

Until Sonos update the Arc for MLPCM you can first try changing pass-through to Auto and see if the C9 realises the Arc can’t do MLPCM and converts it to DD+

if that doesn’t work, turn off eARC and just use ARC so that it forces the TV to convert to DD+ from MAT/LPCM

All these problems will go away once we get the Arc MLPCM update. 

Your explanation sounds very plausible, thanks. What I don’t understand is why a Netlix movie will play in Atmos surround but an iTunes movie will not play in Atmos surround. Are iTunes movies forced to MLPMC output and Netflix are staying in their own native Atmos coding?

Your last sentence implies that MLPCM will come to Sonos ARC? Is that confirmed? If that will be supported then there might even be a chance that I can finally play my Nintendo Switch with surround sound.

 

Almost all services beside Apple’s use Dolby Digital+ w/ Atmos.  

Apple uses a MAT container for Atmos. Strange that the Atmos from Netflix and the Movies app behave differently. The LPMC update on the C9 should affect DD and DD+ content but not necessarily Atmos. I haven’t got any Apple movies but Apple TV+ From my ATV streams fine in Atmos on my C9. 

This is likely because your C9 has been updated to the latest firmware which allows multi channel LPCM pass through from devices like the Apple TV  

Until Sonos update the Arc for MLPCM you can first try changing pass-through to Auto and see if the C9 realises the Arc can’t do MLPCM and converts it to DD+

if that doesn’t work, turn off eARC and just use ARC so that it forces the TV to convert to DD+ from MAT/LPCM

All these problems will go away once we get the Arc MLPCM update. 

Thanks for a suggestion, I tried turning off eARC and just having ARC and Passthrough, what happens then is that Atmos from Apple TV works fine, but any 5.1 content shows up in Sonos App as Stereo 2.0 😞 the same happens with Auto or PCM option...

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