4k blu-rays have no sound on Arc Ultra

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Be nice if it did.

Having popped the Divergent 4K in my Panasonic 420 this morning it reminded me of my history with Sonos and Panasonic so I ran it tonight. 
 

The Playbase I had originally would only yield stereo with Divergent and its DTS-X sound track. Then Sonos added some sort of Dolby Pro-logic support which the Panasonic could add to the stereo track, using the surround encoded downmix option, to give a decent surround mix. It was only when I gave Divergent a spin that I realised it. 

When they added support for the original DTS, my Panasonic TV didn’t support it but 5.1 PCM gave me a great surround experience. 
 

Moving to the G4 and the Arc ultra yields uncompressed Multi-channel 5.1 and 7.1 support. Full DTS-X would add a bit more but they still sound very good. 
 

You state “The Playbase I had originally would only yield stereo with Divergent and its DTS-X sound track. Then Sonos added some sort of Dolby Pro-logic support which the Panasonic could add to the stereo track, using the surround encoded downmix option, to give a decent surround mix. It was only when I gave Divergent a spin that I realised it.”

Sonos and Dolby Pro-logic? Are you sure?

not sure what they added but they definitely added something like that. The difference was immediately noticeable. Dolby pro-logic seems most likely. The app still reported stereo but with noticeable rear sound affects. It probably was able to be added like they eventually added basic DTS support. 

The system will play a soft signal over the rears when receiving a stereo signal. Probably isn’t Dolby Pro-logic though.

To me this has always been the case, but it might have been introduced somewhere before 2019 - my first Sonos device was bought late 2018.

no, this was quite noticeable. Never heard much if any up mixing before hand. A proper surround mix.