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So I’ve been having weird audio sync issues when using LPCM through Apple TV via my LG C9. 
 

The strange part is it’s only happening in some content. 
 

The movie Taken on iTunes is really bad however the movie Chef on iTunes is fine (both 1080p 5.1). The Muse Simulation Theory concert is also fine (4K 5.1). The movie sound city on Amazon Prime is absolutely atrocious. All these problems are rectified if set the Apple TV to output DD5.1 but then I lose atmos. 
 

the delay is inconsistent, some times small (Taken) some times massive (Sound City). 
 

it’s very strange. Anyone else having this kind of problem?

​Hi @Bjmort, 

Thanks for reaching out to the Sonos community and for letting us know about your concern. Let me share some information with you.

Apple TV 4K does not output Dolby Digital Plus (Atmos) signals natively. The content within Apple TV won’t show Atmos support in the title unless the TV reports to the Apple TV it is capable of playing MAT encapsulated LPCM or uncompressed LPCM. You may check Apple's support article Apple TV 4K uses a high bandwidth form of Dolby Atmos that doesn’t work over ARC connections for your reference.

To help you out with the audio sync issues, please follow the steps below and see if it works.

  1. Reboot your Sonos Arc and LG TV
    • Unplug the HDMI cable from the Sonos Arc and the LG TV. 
    • Unplug the power cable from your LG TV, the Sonos Arc, and any connected audio source (such as a cable box or video game console). Wait 30 seconds before you plug them back in.
    • Reconnect the HDMI cable to your LG TV and the Sonos Arc. Inspect the HDMI cable to ensure it’s not bent or kinked and check to see that it’s fully inserted into both devices.
  2. Update the TV’s software (if available)
  3. Adjust the group audio delay - Settings > System > Tap your Sonos Beam > Group Audio Delay and then choose a delay option
  4. Check for Sonos update - Settings > System > Check for updates.

Let us know how you get on with the advice above. Start TV playback for a few minutes and run a diagnostic report. Kindly include the confirmation number in your response for us to check. 

If you have any questions about this. We and the community are always here to help.

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