Is the Digital Sound Output setting on the TV currently set to Auto or Pass Through?

I have it set to Auto now.  I tried the pass through also but the only thing that makes a difference is switching the eARC off.

It is weird.  With pass through enabled  and either eARC on or off, the Apple TV Audio Format setting doesn’t give the option of Dolby Atmos.  With Digital Sound Output  set to Auto the Apple TV shows Atmos available with eARC on or off.  I just don’t get sound with content other than Dolby Atmos when eARC is on.

Set the TV to these settings:

HDMI Input Audio Format: Bitstream

Digital Sound Output: Pass Through

eARC Support: On
 

Set the Apple TV audio settings to this:

Change Format: Off

Dolby Atmos: On

Then do this:

Disconnect everything from the TV and unplug the Arc, Apple TV, and TV from power for a couple of minutes. Plug everything back in but keep everything disconnected. Make sure Simplink is enabled in the TV settings. Run TV Setup in the Sonos app and follow the app instructions. When the app instructs you, connect the Arc to the TV’s HDMI eARC port using the Sonos-supplied HDMI cable. After the Arc has been successfully connected, connect the Apple TV to the TV.

It sort of worked.  I followed your instructions.  After the Sonos Arc, the Apple TV was the first device I connected.  Everything worked as it should.  I then plugged in two other devices the Amino set top box for regular TV and a Roku Ultra.  I went back to the Apple TV and I am still having the problem as before.  I checked pass through and it had been switched to Auto.  I switched back to pass through and did a restart on the Apple TV but the only way I could get sound for every content was to change from passthrough to Auto and turn the eARC off.  With eARC off the only way to get Dolby Atmos from the Sonos Arc was to switch from pass through to Auto.

Thank you for the concise instructions.  I was very hopeful the problem would be fixed.  I may try to repeat your instructions again.  

The Amino or Roku Ultra seem to be causing the problem. Repeat the instructions above and just connect the Apple TV and Roku Ultra and test. Then repeat the instructions above again and just connect the Apple TV and Amino and test.

Not sure what I did but so far sound is working with eARC.  I repeated the process again as you instructed.  At first no sound except Atmos movies so I changed  the audio setting on Apple TV from auto to 16 bit and I got sound on other content.  I switched audio back to auto setting.    Currently I have eARC enabled and I switched from pass through to auto. The audio is set to auto on Apple TV.  So far so good.  Thank you for all of your suggestions.  You have been more helpful than Sonos or Apple tech support.

I am back to using Apple TV with eARC off.  It seems if I unplug all of my devices and power on,  the Apple TV will work the first time I use it but after that only content with Dolby Atmos has sound.  Last night my LG OLED C3 got a WebOS upgrade but that didn’t make a difference.  There is one thing I would mention.  Maybe this will help someone until there is an patch.  My current Apple TV 4K is 128 GB with ethernet connection (3rd Generation).  I also have an Apple TV 64 GB with ethernet connection (Apple TV 4K 2nd Generation).  The Apple TV 2nd Generation works just fine with eARC on.  I plan to call Apple Support in a few days and I will update if I have any success.

I have struggled with this very problem for six months. My set up is an Apple TV latest version, cable box, as the only inputs other than the Arc plugged into the Earc input. my TV is OLED 65 G2.  Other than the current version of the Apple TV… Every other Apple TV works properly with Earc.  
 

LG has replaced the motherboard and power supply twice.

I have followed GuitarSuperstar advice a dozen times.

There is nothing that will work around the Earc issue. 

The Sonos Arc isn’t compatible with the latest version of Apple TV.  

It’s extremely disappointing that Sonos is unwilling to define the technical issue. And I say this being fully aware that the issue may be with LG version of eARC or with the AppleTV.  Even if the issue is with LG or Apple… and not fixable by Sonos… I cannot believe that they are unable to find out what the actual issue is. 

If you leave the cable box disconnected, do you have the same issue?

If the ATV is the only input, the issue does not occur.  if the cable box is the only input, the issue does not occur.  if both the cable box and the ATV are plugged into the input, the issue only occurs on the ATV.

The cable box might be causing CEC interference. Have you tried disabling the CEC setting on the cable box? 

I tried using the Apple TV 3rd generation with my Amino set top box and my Roku Ultra.  Both times I had audio problems with only one extra device attached.  No problems with Apple TV alone.  I tried to disable the CEC (SIMPLINK) but the LG TV immediately switched to CEC on.  The set top box did not have a way to disable CEC.  Does the Sonos Arc require CEC to be on?  Anyway it would be very inconvenient if I could not control all of my devices with the tv remote.  

I am back with my Apple TV 2nd generation and no problems.

CEC can be a mess because there is no exact industry standard with respect to how multiple devices should interact. Sometimes the best workaround is using a CEC blocker on one or more devices. Disabling CEC in a device setup does not always workout because this may also disable features such as advanced audio.

I have tried disabling CEC on the TV itself. At first this allows the ATV and the cable box to operate properly while going back-and-forth between the two. But fairly soon it reverts to the issue with the ATV.  however the pass through setting never works, it must be set to Auto.

Bottom line: Reverting back to using ATV second generation is the only thing that works.
 

This leads me to my conclusion that it is the ATV third generation that is the source of the issue. 

Having said that… I still believe Sonos should troubleshoot this and find the source of the conflict with ATV 3rd Gen

I ordered the Lindy CEC less HDMI adapter.  I inserted it on the HDMI cable for the Apple TV.  It did not solve the problem and I am back to using the 2nd generation Apple TV 4K instead of the 3rd generation.  I am not sure that the CEC less adapter did what it was supposed to do as I could control my Apple TV with the LG remote with the adapter inserted.

I am not surprised at your result. There is a definite conflict between Sonos and Apple TV third generation. What I do not understand is why doesn’t Sonos identify the conflict. Even if the conflict points to Apple… The fact remains is the Sonos Arc is not functional with The Apple TV third generation. Is that OK with Sonos that their system doesn’t function with an apple product that thousands of people own?

It’s odd, I use the Apple TV third generation though my Vizio TV to my Arc without any issue whatsoever. 

@rmartin7 Have you tried disabling the “1-touch play” setting on the Roku Ultra? Or use the Lindy CEC less adapter on the Roku Ultra or the Amino box?

I disabled the 1-touch play.  No effect.

I went through the entire setup process as you described earlier.  With only the Apple TV 3rd generation connected everything worked.  I then added the Amino set top box with the CEC less HDMI adapter.  The issue with no sound from non Dolby Atmos media on the Apple TV reappeared.

I am back to using my Apple TV 2nd generation with no problems.  

I will be busy next week.  I haven’t really worked much with Apple support and I haven’t called LG support so that will be my next step.

One thing I would mention.  I tried upgrading the Apple TV 3rd generation to a beta version of TVOS.  That didn’t solve the problem and I had major issues with the upgrade.  I found out after the fact that the Apple TV cannot be downgraded to the public release of TVOS so I ended up getting another Apple TV 3rd generation.  All of the troubleshooting has been done with TVOS 16.6 on the new Apple TV 4K 128 GB with ethernet connection.  So I would not recommend trying beta versions of TVOS.

I have one ATV third generation on 16.6 and one ATV third generation on 17.0 and neither affects the audio issue we are discussing.  I have zero issues with TV usOS 17.  Love it in fact.  

Apple will allow me to return the ATV third generation, but could not identify the issue with audio and the LG TV. LG customer service is an all out nightmare. I wish you a lot of luck there  I’ve been dealing with them since March. My case was escalated to what they call presidential liaison, and that is actually worse than the regular customer service. 

I truly believe Sonos is the only company in the triad that cares enough to really troubleshoot this issue.

The difference is the LG vs. Visio.