Apple TV 4K 5.1 surround sound not working

Since I ran into this issue as well and figured out how to solve it, I thought I’d update this thread for anyone else that may run into the problem in the future. First, it is not clear whether the issue stems from an update to the Apple TV or the LG C9 set (or possibly other LG sets as well), but the issue was not present since the beginning and so was introduced through updates. Now on to the problem.

LG C9 has two modes for audio pass through, either Bitstream or LPCM, and offers two connection modes, ARC and eARC. ARC is only capable of carrying 2 channels of lossless signal, while eARC can carry 7 channels of lossless signal without issues. What Apple TV does is it decodes the 5.1 signal and passes lossless LPCM downstream (lossless is used loosely here since the original signal was lossy, hence lossless is just a term for “uncompressed”). The problem is that at some point either Apple TV stopped passing metadata to the LG C9 that would tell it that it is really receiving 5.1 multichannel audio, or LG implemented a change in the firmware that led to this. (To make matters more frustrating, appropriate data is being passed when Atmos is in question.)

Anyway, when using ARC on the LG C9, the absence of any additional metadata means that the data stream contains more data than can be passed on using ARC, hence it downmixes to 2.0 channels only and passes that via ARC to the AVR. (On the other hand, if one is using eARC, LG will just pass through the full LPCM stream to the AVR, as long as the AVR too has eARC.) More details on ARC and eARC are below.

https://www.cnet.com/news/hdmi-audio-return-channel-and-earc-for-beginners/

So what is the fix? Really, only a few options are possible. First option is to use eARC instead of ARC if possible. Second option is to go ATV > AVR > TV. Third option is to extract the audio stream from the ATV signal and split it off to the AVR while sending video to the TV using an HDFury AVR Key or Vertex device, is similar. Fourth option is to use a device like Thenaudio SHARC eARC to “add” eARC capability to a signal stream to a receiver that is only capable of ARC, thereby allowing eARC to be enabled on the LG C9. No other fix is possible.

Definitely seems to be an LG issue. Read a suggestion on the LG forums to change pass-through to Auto and now the sound is coming out of the correct speakers. I noticed when using the Sonos app that my xfinity cable box no longer shows up as outputting DD5.1 but now shows as Dolby Multichannel PCM 5.1 - looks like the Auto setting is forcing some audio processing by the TV. Atmos content still shows up as Atmos, so at least that’s all good. Looks like the pass-through setting on the CX isn’t truly passing through the native signal, but somehow mucking it up enough to confuse the Sonos.

does not work … does not output properly …

So what happens instead? Silence, muffled sound, missing channels, anything else peculiar?

It works fine when the content is Atmos

Including Dolby Atmos from the Apple TV content? I would have thought than any device that can process Atmos from Apple TV, would easily process 5.1 discrete channels. How weird.

As a test, what happens when you force the Apple TV to use Dolby Digital 5.1 for Audio Format?

Visio soundbar

Which one?

I have an LG C9 connected to a Sonos Arc using eARC (Digital Sound Out is set to “Pass Through ”) and anytime I try to play 5.1 content through the Apple Movies/iTunes app all I get is silence. I am running tvOS 14.6. If I manually force the AppleTV to output DD5.1 using the Change Format option it works fine, but then I have to remember to change it back when I play Atmos content. Sonos is running latest version (13.1.4) and LG C9 is running latest version (03.23.06). Definitely feels like Apple changed something as it was all working fine a few months ago - very frustrating when it should just work.

The implementation of eARC is a mess. I don’t think it is an Apple issue. I think the TV manufacturers need to work more closely with the receiver / sound bar manufacturers to better implement the eARC specification on their respective devices. eARC is still relatively new and the different manufacturers are still learning how to properly implement it. Samsung will say that their sound bar works perfectly with their TV, just as LG will say the same, but the TV manufacturers need to do more testing with Sonos, Denon, Sony, etc. to clean up their code. In my case, I put a lot of the blame on Sonos too. Once I turned off eARC on my LG CX TV, everything worked fine. I just don’t get all the extra features of eARC at this point.

Latest firmware for the C9 is 05.10.15. I would look into updating before troubleshooting further. Sorry I can’t be of more help.

Hi MIheatplaya25,

We understand you're running into an issue setting up surround sound with your Apple TV. Have you checked for possible firmware updates on all of the non Apple devices involved? Be sure to follow the steps in this article when setting up your surround sound system with Apple TV.

Play audio in Dolby Atmos or surround sound on your Apple TV

Have a good day.

If this issue persists for iTunes Store content or Apple TV app Channels, then contact the experts at Apple Support about that.

For issues with third party apps, contact those developers.

For AirPlay/Home Sharing encodings-not-by-Apple, the issue may be with the source file(s), and Support may not be able to assist you with that.

Switching between ARC and eARC is done in the TV settings. You need to look up the details in your Q90 manual. Note that “silent” is not the same as defaulting to 2.0 so I would actually say that you’re not dealing with the same issue and would suggest that you factory reset your whole setup and reconnect everything to see if the problem persists before digging further. The reason why I say this is because if all you are getting when the audio is something other than Atmos is silence, that means that no actual audio stream (or an unsupported audio stream) is being passed to your sound bar. Full disclosure also, I have no experience with sound bars. I only ever use AVRs.

That’s exactly how I’ve been handling. Only thing different is that the silence isn’t consistent. Sometimes I do get 5.1 pass through. It’s even been working fine on a show/app and then it automatically switches to the next episode and it breaks and I have to switch it to Dolby Digital. Going just keep switching manually until they fix because it’s definitely a software issue.

LG just updated their firmware for the CX to version 03.23.15 and it seems to be working fine now.