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I just recently purchased a Sonos Arc for my 2017 LG B7 OLED, which is Atmos and ARC compatible. 

I have a brand new Chromecast with Google TV and an XBOX One X (both Atmost compatible) hooked up to the TV, then running audio to the Sonos Arc via the HDMI ARC out (not eARC). All devices and TV set to bitstream/non-PCM. 

When I use my LG TV’s internal streaming apps, audio/video sync is perfect, including Atmos content on Netflix, Vudu etc. Verified via Sonos app that it is receiving full Atmos signal. 

When I try to listen to Dolby content coming from my external devices, the audio is noticeably behind the video.

  • Dolby Atmos content from the Chromecast or Xbox works but there is significant delay to the point of unwatchability
  • Non-Atmos Dolby 5.1 content from Chromecast or Xbox is a little bit delayed… noticeable if you’re looking for it.
  • PCM audio from Chromecast or Xbox has no sync issues. 

I’ve messed with all the various audio settings in my TV to make sure any sort of additional processing is removed. I’ve also tried playing with the delay, because LG does offer the option to move sound earlier, but moving it as early as it goes (-5 in the settings) doesn’t fix it enough on Atmos (also it’s not a great fix given that the TV is applying this negative delay to all content on a given input uniformly regardless of audio format. 

I’m totally at a loss on what to do. Buying some third party audio splitter like the Sharc makes the elegance of the Sonos a moot point. And this seems like a pretty systemic issue with many popular TV manufacturers. Even with all the various Sonos and Reddit forum posts, plus this Guardian article (https://www.theguardian.com/money/2020/sep/06/that-syncing-feeling-when-your-soundbar-lets-you-down), I’m surprised more people aren't complaining, because I don't think my TV/component combo is any sort of “edge case”… it’s pretty common. Are most people just using their TV’s streaming apps exclusively for Atmos content and therefore not seeing the delay?

From what I understand, even if I upgraded to a new TV like the LG CX that has HDMI 2.1 and eARC, this lip sync would still be a problem because neither Xbox One X nor any streaming box is HDMI 2.1 compatible so it couldn’t utilize more advance synchronization on those devices. 

I really love the look and the sound and the simplicity of the Sonos Arc, and I don't want to return it, but I may be forced to exchange it for a soundbar that doesn’t rely on ARC and just does a more standard receiver-style HDMI passthrough to avoid these audio delays. 

Does anyone have any other suggestions before I throw in the towel?

Thanks!
Ben 

Hi.  The Arc plays what it gets when it gets it, and lots of TVs pass the audio from external sources with a lag (although this may be format dependent).  The adjustment in the LG sound settings is of course not an acceleration of sound but a delay in picture - an option not open to Sonos.

I am not sure that Sharc have a solution for this.  I use an HDFury Arcana, but that was primarily because my E6 (2016) LG OLED TV does not have eARC and neither does it process Atmos (even on DD+).  Fixing the audio sync issue was a bonus consequence for me (as the Arcana bypasses the TV for audio),

There are other users on the forum with much better AV knowledge than I, who will be able to offer further comment, I am sure.

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