https://support.sonos.com/s/article/4945?language=en_US

Note that Dolby Atmos and Dolby Multichannel PCM are passed to Sonos using the Dolby MAT container. Dolby Atmos is Multichannel PCM that includes Atmos object data. Dolby Multichannel PCM does not include Atmos object data.

So yes, there is a difference in the format, and you are probably getting slightly better quality with the MAT format over DD+, but you are still getting the same audio channels either way.  I would leave the TV setting to passthrough.

Both will be the same. If you go into settings and about my system when playing something, you will see that is will also show Dolby Atmos (dd+) with passthrough enabled. Dolby Atmos (true hd) is the best format you can get, but no streaming platform plays lossless codecs, only disks / rips will. 

But for me that is not the case, and is the reason I posted here- with passthrough enabled on the TV, the about my system shows Dolby Atmos (not Dolby Atmos (dd+). That is where I am confused. It only shows Atmos (DD+) if I have passthrough off.

But as you say, since streaming cannot play lossless, even though it shows Dolby Atmos (not DD+) I am still not getting “true” Atmos- is that correct??

You still get the Atmos soundtrack even with Dolby Atmos or Dolby Atmos (dd+) as yours is showing (the height channels). True HD is just a lossless codec. Comes down to your ears as well haha. While some say the difference is marginal, I can certainly hear a difference between DD+ and True HD. But as per original post, keep passthrough enabled. 

So are you basically saying that whether the app reports “DOLBY ATMOS” or Dolby Atmos (DD+) those 2 are basically the same? And even if I am seeing DOLBY ATMOS on the app (without the DD+) I am still not getting the “true hd” lossless Atmos as long as I am streaming.

Is that correct?

That's correct yes as streaming platforms don't upport lossless (Dolby Atmos true hd) content. There is one platform that supports Dolby Atmos True HD and also has the highest quality of any movie format and that is Kaleidescape (https://www.kaleidescape.com). However it is absolutely insane amount of money as you need their hardware to be able to purchase / rent the movies. However if you want quality that is even greater than UHD disks, then this is the thing to buy. 

Back on topic chances are with it set as auto, it might be doing some audio conversion and the quality may be slightly lower. 

If you try some other applications like Amazon prime / netflix (if you have them). You may find that with auto set you might get an output like Dolby pcm 5.1 where as with passthrough you will get Dolby digital plus 5.1. 

Can't really give you a full concrete answer as to why you don't see the DD+ with it on auto, however I am guessing it is doing its own conversion somehow. 

Maybe run some tests with some good Atmos scenes and see if there's any improvement on either, but either way they will both be the lossy type of Atmos. 

Thanks- yes, I have listened to various Atmos programming, and I can’t tell a difference when it reports Dolby Atmos vs Atmos (DD+). So I guess I will just stop worrying about it- lol

Thanks for your assistance- much appreciated.

I don’t think TrueHD, which is usually only found on blueray disks, is relevant here.  The source is an Apple TV, which I believe uses Dolby MAT, which Sonos can play.  So when your TV does passthrough, it doesn’t adjust the audio at all, and Dolby MAT is sent to your Arc and will label as ‘Dolby Atmos’...see the link I put up earlier.

If you turn off passthrough, your TV will convert the MAT audio to DD+ before sending to your Arc.  You still get Atmos, but in the DD+ format...again, see the link.

So I would leave passthrough on, as you’re cutting out the additional processing on the TV side that you do not need.

Thanks for that- that makes perfect sense

While I have you guys, one more question- because of an annoying audio delay when watching Directv content, I have to turn the EARC setting on my HDMI port to OFF (It is a setting in the Sony A80J hdmi settings). The Arc is still connected to teh earc port on the TV.

Even though I have this set to OFF, I am still getting Atmos showing in the sonos App whenever I watch or listen to Atmos content.

So am I losing anything by having this setting OFF? It doesn’t appear that I am, but not 100% sure.

If you don't have any devices that can do lossless audio, then it won't harm to keep it off. Think the Sony can do all the codecs so you don't need to worry about converting to lpcm. However I'd try find a solution if possible to keeping earc on and sorting the lip sync issue out. 

Thanks again- that is what I thought. Just to be clear though, the issue I have with the Directv is not a lip sync problem, but just a very annoying 1-2 second audio delay whenever pausing/unpausing live programming or changing channels. For days I tried everything possibly could to fix it with no success until I accidentally discovered that turning that earc setting off completely made it go away. Not sure I understand why but it definitely fixed it. I had the same Directv box with my old TV which was hooked up to a Sonos beam I used before getting my Arc, and it never had that problem.