Dolby 5.1 content outputting as multichannel PCM 7.1 (since LPCM update)

app or system update?

*Just checked for updates and no updates available , I’m on 12.2.1, Im guessing you only just updated this or do you have newer version?

I’m telling you guys, to me (and this is now my own personal theory) is that the Apple TV 4K is the reason none of this works like it should. Based on these facts. 
 

1. using local Apple TV native App on the LG CX doesn’t have sound or judder switching in between different audio formats - although the audio is not the same or yield as good of audio as what can be provided via an actual physical Apple 4K TV device 
2. Physical Apple 4K TV only has HDMI 2.0 - speaking in technical terms like as if in I.T. You can can have a GIGABIT router but if you feed a 10/100 switch whatever devices are plugged into the 10/100 switch will only get 10/100 AND NOT GIGABIT speed (bottleneck) 
3. This was happening on the Bose 700 series (which it didn’t have Atmos BUT DID HAVE HDMI 2.1) 

I’m chalking it up to ATV4K at this point. If I’m wrong I’m wrong it just makes logical sense and eliminates all other possibilities as every device (TV/cables/Sonos Arc) provides HDMI 2.1

It happens on my Oppo 203 and Xbox series x as well, which the latter is hdmi 2.1.

@ledzep1

I have a PS5 (which it too has HDMI 2.1) as it doesn’t offer DV nor Atmos. 

Key thing I’ve noticed with the Apple TV app on the PS5 (like the Native app on the CX) is there is no way to go into the Native Apple TV app and adjust any sound settings within the “thin client” which is provided on the CX/PS5 thin client apps - can’t speak for Xbox. 
 

Thin client ATV apps are a great option but aren’t relatively based or designed as a replacement of a Physical Device such as a player (Apple 4K TV) which was designed to output specified settings and overall architectural design. 
 

kind of like playing Madden Mobile vs Madden on a Xbox or PS - just isn’t the same thing/experience. Might have the same name but isn’t the same thing. 

And in no way is this meant to sound argumentative. 

Think of it this was as well. 
 

If the CX / Sonos Arc / and the current physical Apple 4K TV all have HDMI 2.1 and your HDMI cables were older and outdated and don’t support HDMI 2.1 then the bottleneck would be your cables. 
 

I believe Sonos has actually held their end up by providing this update to support all these new features and that based on isolation it isolates to the ATV4K. 
 

I believe this not be a software issue but rather a hardware issue with the limitations being that of the HDMI infrastructure built within the current ATV. 
 

As of writing if you do your research no one is claiming they’ve gotten this setup to work with everything setup like the way we have it. In addition to the lack of HDMI 2.1 on ATV4K could also explain the handshake not happening properly switching between Atmos and other audio formats. 

I’ve been having the same problem recently with my AppleTV 4K. The file playing is a Dolby Digital Plus 5.1, but according to the Sonos app it’s playing as Multichannel PCM 7.1. 
Result is usually that I can’t hear any speech in movies, only the music…

If I play the same file directly from the TV, then it seems to work correctly… so not sure if it’s maybe an issue with the AppleTV…. I’ve tried Infuse, Plex, Netflix, they all suffer from the same problem.
 

using tvOS 14.2

Sonos Arc + Sub + 2x One’s with version 12.2.1 

AppleTV → HDMI → LG OLED65CX6LA → eARC → Sonos Arc

@Veldkornet

As I stated based upon my own personal belief is this entire problem lies within the Apple 4K TV and it’s lack of HDMI 2.1 support which rests on its own hardware deficiencies as it’s only capable of handling HDMI 2.0. 
 

I have heard the LG CX has a new update out (3.11.41) which hasn’t pushed out yet to my LG CX 65’ but am interested to see if it can offer anything. 
 

Hardware is Hardware so if my theory holds true no software/firmware will fix a hardware port designated and designed only for HDMI 2.0 (ATV4K) there is just no way around it as it’s embedded and fixed into the hardware itself which so far is the only culprit amongst all devices TVs/cables/and other peripherals THAT HAVE HDMI 2.1 support that seems to lack it. 

Hmm, my CX is still on 3.11.25, I’ll keep a look out for it though.

What a pain in the ***, the AppleTV was working so nicely until recently. 

You mean 3.11.30?

That was released to a lot yesterday, but it doesn't fix the issue. Also I think I replied to you when you mentioned its the fault of the apple tv 4k because a lack of hdmi 2.1 support, if that’s the case why does my series x (hdmi 2.1) exhibit the same issue

I have the series x set to uncompressed 5.1 and sonos app reports multichannel pcm 7.1.

I think the issue lies with the LG CX or the Sonos.

@ledzep1

I believe I responded to you as well. I have a PS5 (HDMI 2.1) but doesn’t have Dolby Vision nor Atmos (which is ridiculous and makes it irrelevant to your question) 

What I believe with respect to your Xbox is you downloaded the “THIN Apple TV app) on your Xbox. 
 

If you go within your Apple TV App on your Xbox and go under settings you’ll notice their is no “sound options” LIKE within an Actual Apple TV to make any sort of output adjustments in regards to sound (JUST LIKE THE BUILT IN THIN CLIENT ON THE LG CX) 

Because BOTH your Xbox and even the LG CX lacks this feature it rules out your HDMI 2.1 your Xbox is capable but handicapped by the THIN APP at this point JUST LIKE the LG CX (which in all honesty should be the FULL PROOF WAY of getting around this BUT because it’s a THIN WATERED DOWN VERSION of Apple TV you get handicapped by the Limitations of the App itself. 
 

I know it seems ridiculous but THATS EXACTLY WHAT IT IS.