True HD Atmos as PCM Stereo instead of Multichannel

You are right this solves the problem but doesn’t explain the weird behavior in the first place. Some people might want/need to keep it on Auto and are stuck with this problem.

It’s not an infuse problem but rather an issue with how the TV handles audio it receives and forwards to eARC. Problem doesn’t exist if you go straight into a receiver or a soundbar with extra HDMI inputs.

It could also be an LG problem. I had issues with multichannel PCM and LG TVs in the past. You could set it to auto and then check via the HDMI diagnostic menu if the TV receives Stereo PCM or multichannel PCM from the ATV. I don’t know what it’s called in the English interface but it should be sth like ‘programs’ → ‘search programs’ you need to have this point highlighted and then press 1 on the remote for 5 times. The upcoming menu needs to be expanded in the HDMI section, I’m sure you’ll find what I mean.

LG OLEDs can’t transcode Dolby TrueHD audio, which is why the Digital Sound Output needs to be set to Passthrough, so it travels from the ATV to the soundbar untouched by the LG TV. Setting the Digital Audio Output on your LG to Passthrough allows your ATV to do all the work and send the file in an ‘as-is’ state to your soundbar.

For any future readers this is only supported on devices using eARC, not ARC.

ARC would have you connect your streaming device directly into your soundbar, but with eARC we can avoid this.

As to why it happens: There may be some “miscommunication” between the ATV & LG when set to Auto because the Infuse app is down-converting a Dolby TrueHD source to Multi-Channel PCM. This process may be “confusing” the tv in choosing how to transcode the codec, thus, defaulting to Stereo.

Hope this helps.

I have a few movies rips that have an Atmos 5.1 eAC3 track and a 7.1 eAC3 track.
I’m using Infuse on an Apple TV 4K. Samsung Frame 2024 and an Arc Ultra based setup.

When I choose the Atmos track everything works as intended. I see the logo in the SONOS app. But when I choose the 7.1 track, it gets « downgraded » to stereo PCM as shown in the app.

I’m wondering if it’s a bug? A configuration thing? An incompatibility? Anyw views?

Thanks!

I moved your post to a related thread which has more info on what may be happening, and some things you can try to resolve the issue.

Thanks James. I had a look at options, and tried various things, to no avail… The track in question is E-AC3 7.1, not True HD. I’ve tried rebooting the Apple TV and changing options on the TV, but it didn’t change, the track still outputs as Stereo PCM

I’ve never been able to get a 7.1 atmos track to work. I’ve read on other forums that the AppleTV dolbyMAT is limited to 8 channels so either 7.1 or 5.1.2. It’s possible your Sonos doesn’t support 7.1 PCM?

Side note I’ve never tested a 7.1 track that doesn’t have atmos on it.