If the Sonos App is showing Dolby Atmos on it’s ‘Now Playing’ screen and on the ‘Audio In’ next to the Arc device too in the ‘about box’ in the App settings, then as far as I can ascertain as a user, the audio input (according to Sonos) is certainly Atmos audio.

I can’t personally account for what your TV/FireTV display is showing - that’s something you would perhaps need to ask of LG or Amazon Support Staff, or maybe users of those products. As a user of a different LG TV model (C9 OLED) however - the device settings you have mentioned in your post do sound correct to me.

In my own case I have tested my Sonos audio output by playing sample dolby Atmos audio files and what I’ve seen displayed in the Sonos software, usually corresponds with the type of audio selected.

Here is a link for a sample Dolby Atmos audio test-tones video that you can perhaps use/test with your own devices…  

CLICK HERE

I hope the above is a start to help you find the answers you’re looking for.

The FireCube (Firestick does) should have an internal Atmos test signal buried in the diagnostic menus.

Maybe:  Settings -> Display & Audio -> Audio and Video Diagnostics -> Play Dolby Atmos and Vision content

Yes, I discussed that exact test in detail in the first paragraph of my original post. While the Diagnostic states that my TV/Equipment is capable of all audio formats, including Atmos, MAT, DD+, and DD, when that test is played I do not get the Atmos popup on my TV, and the TV information will list “Dolby Audio” while the Sonos app states “Dolby Atmos” on the basic volume page.

Thus, the confusion still remains. It seems very odd to me that my TV would not reflect the audio format being Atmos when it does so anytime I use my Playstation 5 (though this popup appears immediately when my PS5 is used, regardless of the content being played, and furthermore, I use a headset when gaming, so I’m not concerned much with the audio format that is output to my Sonos system. I have not tried to test out any Atmos media using my PS5 but maybe that would provide more, potentially useful, information) or when using the built-in Smart TV apps.

Perhaps using the test file from @Ken_Griffiths will help to reveal the truth of the matter, but I will have to look into how to play this file properly on my Fire Cube to rule out any issues from an improper test. It could be that what my TV describes as simply “Dolby Audio” is indeed Atmos as reflected by the Sonos app. But why it describes it this way rather than simply as Atmos is what is confounding me at this stage.

There’s a known bug with the Fire TV Cube 3 with some TVs and Sonos Arc.  Specifically, the diagnostics shows the system is fully capable of Atmos, but no Atmos plays from any of the apps.  I’ve found it with my Samsung, but there are other reports.  I was on the phone with Amazon after a scathing review, and they escalated to Engineering.  After I worked with them, I never heard back, and to this day, the Cube 3rd Gen still doesn’t give Atmos.  See this forum post:

https://www.amazonforum.com/s/question/0D56Q0000ADhzARSQZ/new-fire-tv-cube-3-no-atmos

Here in the U.K. I pay the monthly/annual subscription to Prime Movies - I think I pay £99 annually or thereabouts. That subscription used to provide Atmos audio, but that audio codec has been taken away now and they’ve also introduced ads.

So I now have to pay another £3 (approx.) per month to remove the ads (there’s no annual subscription) and that has also reintroduced Atmos audio too. 

Same in the US.  Ad-free, Atmos, and HDR/Dolby Vision are extra cost. 

Thanks for this insight. I have also been looking into issues with the Fire TV Cube 3 and it’s problems with Atmos content. Disappointing that Amazon is either unwilling or incapable of addressing this problem. Even more so considering the Gen 2 Cube does not have the same issue. Also, very useful to know that people are reporting this problem with equipment other than Sonos, further hinting that the problem is with the Cube itself.

It was because of these findings that I came here to ask the question. I have my doubts that my Fire Cube is playing Atmos content, based on the experiences of others and the information relayed to me by my TV. That’s why I came here to ask why there would be a discrepancy between what audio format is displayed in the Sonos app and what is displayed by my TV. While I am doubtful that this is the case, perhaps the Cube is actually outputting Atmos formatted audio, but for whatever reason my TV cannot tell, but the Sonos equipment/app can. I will try to test this by simply playing the same piece of content using my Cube and then using my built-in TV apps. If anyone has a suggestion for a piece of media on any streaming service that clearly demonstrates the differences between Atmos and non-Atmos audio, even better if I could be pointed to a time stamp of a specific scene, I would be deeply grateful if you could pass along that information for this test.

I will be sure to report back my findings if I manage to draw any conclusions of which I am confident. My hypothesis is that the Fire Cube is not playing Atmos content, despite what the Sonos app may say. If I find this to be true, I will also add my voice to the complaints being lodged at Amazon regarding the problems with their “Flagship” and “Most Powerful” Amazon Fire TV device. I, too, am appalled by the greed of Amazon surrounding their transition to ad-supported video for Prime TV, a service that I imagine is primarily enjoyed by those already paying the increasingly steep fee of a Prime Subscription. The fact that they also chose to lock Dolby Vision and Atmos formats behind a paywall serves as another gut punch to their paying subscribers. And that is all assuming that they can actually play Atmos content through their devices. Makes you wonder if they paywalled Atmos in the hopes of fewer people actually noticing their technological deficiencies surrounding Atmos support on their devices...

Remember, there may be a difference between what your TV is receiving, and what it may be sending out to the Sonos. I’ve certainly seen TVs that aren’t capable of passing through everything that they receive, and even more frustrating, playing a format properly on internal apps that they can’t receive via HDMI.

One more ‘warning’. The Sonos reports the type of carrier in use. That doesn’t mean the source is using all of that carrier. 

I used to get pre-season football games, sent to me by my local station in a Dolby Digital format, but the source material was in stereo only. So my Sonos was sending empty data to the center channel and subwoofer channel, and some pretty useless data to the surrounds. It took me an hour of fiddling before I finally realized the source was a stereo signal carried on a Dolby Digital carrier. 

One of the reasons I always recommend an action movie for testing. Even the news was in Dolby Digital, but with nothing being sent to the surrounds. 

@lattanzion,

What audio format does the LG TV show if you change the LG TV HDMI-ARC digital sound-out from ‘pass-through’ to ‘Auto? I’m just wondering if that may show anything different when playing Atmos audio from your FireTV Cube device?

@Ken_Griffiths 

I’m not sure why I never considered even trying this as a troubleshooting option, despite most of the conventional recommendations to have it set to pass through. Shockingly (to me, at least), when I change the setting to Auto and play Vision/Atmos content, the popup now displays “Dolby Vision” and “Dolby Atmos through Soundbar.” If I set it back to Pass through, no Atmos popup.

You may have saved me from endless frustration and (presumably) difficult dealings with Amazon over this issue.

It’s hard for me to tell for sure, and this may not even be something that is exclusive to Atmos content, but there appears to be a slight audio/video de-sync that is mostly notable when actors speak. But, luckily, the Fire TV Cube does have a setting to address this. And while I’ve seen many people complain about this issue using Sonos systems and specifically Atmos content, being unable to fix it as the Sonos app and many TVs only provide the ability to add delay, it seems the Fire Cube can both add delay or do the opposite. This does not seem like an unsurmountable challenge to dial in perfectly.

Thank you, @Ken_Griffiths. What should have been an obvious test for me to perform simply never crossed my mind due to all of my research pointing towards having this set to Pass through, and the inherent logic in doing such. My TV even had an update (no idea what for, would have to look at patch notes but why bother) and putting this setting at Auto worked both before and after the update.

So to anyone with the LG C-Series OLED TVs, or maybe any of their OLED lineup encountering this issue when using Amazon Fire devices (possibly only applicable to the Fire TV Cube Gen 3), I encourage you to test out whether setting “Digital Sound Output” in the Advanced Sound settings to Auto and seeing if this fixes any Atmos difficulties.

And furthermore, the Sonos app continues to display “Dolby Atmos” as the format being played. So the mismatch between what my TV displayed and what the Sonos app displayed no longer exists.