Sonos Arc and 7.1 Downmix to 5.1

I think this is/was an issue with some LG CX TV’s, see this thread for additional info:

The above link runs into a slightly longer thread, which seems to infer that some devices send LPCM 7.1 audio ‘through’ the LG CX TV if it’s HDMI sound-out is set to pass-through,  and that Sonos plan to possibly downmix the channels to 5.1 in a future update (no information about when that might happen) - at least that’s how the thread reads to me at a quick glance.

Maybe changing the audio-out settings on the A/V sending device, or changing the TV HDMI Digital Sound Out to ‘Auto’ (instead of pass-through) to let the TV process the audio before it gets to the Sonos HT, will help to fix the issue in the meantime, if it is perhaps causing you an issue.

Yes this is still an issue and an infuriating one at that. Sonos has not yet announced the downmix feature and LG are completely silent on the issue which is entirely unsurprising. 

yes its still an issue.

if you see “LPCM 7.1” in the Sonos app then 100% the sound coming from the speakers will be messed up. Right now, its needs to say LPCM 5.1 or its going to sound wrong

I thought it was in the testing as a “fix” sometime last year, funny that Sonos has now labelled it as a “feature”. 

I have got a bit lost with it all now as there was a few issues with LPCM at the time these issues were first reported, which is why it would be nice of a Sonos support rep on here to respond, by saying if a fix/feature is in the works, maybe its an LG issue, then so be it, just would like some response.

Is it really that hard?

I bought the Sonos ARC, sub and symfonisk frames for rear duties just a couple of days ago and although I am happy with the sound I am having issues regarding DTS Blu-ray. I have set my Blu-ray player to output DTS master audio as LPCM but the app shows PCM 7.1 not 5.1. Does this mean the ARC is ignoring 2 channels and not playing audio correctly? I have a Sony a80j OLED TV which is set to passthrough and have had zero issues with my previous Samsung q950t soundbar connected. I am not new to home theatre and have had various systems throughout the years from full atmos installs to various HIFI separates and sound-bars so I know it’s not user error or setting problems. I was under the impression I could get DTS Master audio via LPCM without issue but now I’m not so sure. Any ideas?

There is a known LPCM 7.1 to 5.1 down mixing issue with the Arc. Sonos is aware of this and is working on fixing the issue. Some people have reported they can clearly hear two channels missing from the surround audio, but I can’t tell the difference. I have tested the surround channels with a DTS 7.1 Sound Check on a DTS demo disc and all four surround channels play out of my two surround speakers correctly. But I am also using an HDFury Arcana which might be the reason why I don’t seem to be experiencing the down mixing problem.

I am replying to follow for any updates as this is what I’m waiting on as well. LG C1 and pass through causes 7.1 on a 5.1 system. Hoping they fix this soon!

Also very interested in some kind of update on a solution to this. 

Is this a problem for the LG G1?  Are we supposed to keep the TV audio set to auto still?  If my source file is a TrueHD 7.1 Atmos remux, do I still want my Sonos App to show Multichannel PCM 5.1?