Hi @Raz7
Welcome to the Sonos Community!
Off the top of my head, I can think of five different places where settings could affect which audio codec the Arc receives:
- The Plex server’s audio transcoding settings
- The Plex app’s audio output settings
- The audio output settings of the device running the Plex app (if not the TV)
- The TV’s audio output settings (and passthrough capabilities, though if the TV hasn’t changed, this won’t change)
- TrueHD needs eARC to be enabled in the TV settings
All I can suggest is that you go through each of these and check what’s set. If the app shows “Dolby Digital + 2.0” then that is what is coming down the HDMI link - we do no conversions.
For what it’s worth, I have experienced similar issues (Dolby 2.0) with my nVidia Shield Android TV box and the Emby service/app (similar to Plex). The issue turned out to be that both Emby and the Shield were attempting to convert unsupported formats (I have an Amp which doesn’t support Atmos/TrueHD) into Dolby Digital. Disabling the conversion on one solved the issue, though I do get the occasional movie where I have to swap what performs the conversion to get audio.
I have Plex too, and have found it more difficult to get the desired results on it than on Emby, but I haven’t tried very hard as I prefer the Emby interface and free-tier features.
I hope this helps.