I’ve been having a bit of an issue with my LG CX + Apple TV + Sonos Arc and have been searching for solutions to no avail. 

Every recommendation I’ve come across has been to set the Digital Sound Out to “passthrough” to receive Atmos unprocessed to the Arc via the TV from the ATV 4K. But when this setting is selected, the image clears out momentarily and the Dolby Vision notification disappears from the screen and the HDR logo appears in it’s place. The screen also appears much brighter.

Changing the Digital Sound Out to “Auto” fixes this. But I’m not sure why selecting “passthrough” for an audio output is impacting the video at all.

I thought this might be an issue with the Apple TV, but an Xbox Series X performs in the same manner. Oddly, the internal TV apps can be set to “passthrough” for the Digital Sound Out and the Dolby Vision works fine.

I’m trying to get the highest quality sound to the Arc without also compromising picture quality.

The audio settings for the LG CX are:

Sound out: HDMI ARC

HDMI Inout Audio Format: Bitstream 

Digital Sound Out: Auto

eARC: On

The Apple TV is set to:

Video: Enable Dolby Vision

Format: 4K SDR

Match content: Range and frame rate

Default Audio Output: TV speakers

Audio format: Auto, Atmos available

The system is all connected with new 8K cables, so that should not be an issue.

Any insight into what could be causing this would be greatly appreciated. Thanks.