Dolby Atmos codecs on Sonos Arc

Hi @takriel.

Thanks for reaching out and welcome to the community! Let me check it for you.

Dolby Atmos can do two types of surround sound signals: 

• Dolby TrueHD

• Dolby Digital Plus (DD+)

Most Dolby Atmos audio can be played through HDMI-ARC using the Dolby Digital Plus (DD+) codec. HDMI-eARC is required to play lossless Dolby Atmos audio using the Dolby TrueHD codec.

HDMI eARC supports the latest, high-bitrate audio formats such as Dolby Atmos, Dolby Digital Plus, and Dolby TrueHD.

ARC and eARC are protocols responsible for sending audio over an HDMI cable to home theater sound systems like Sonos Arc.

Arc uses the Enhanced Audio Return Channel (eARC) next-gen version of ARC implemented in HDMI 2.1.

The main benefit of eARC is greater bandwidth and speed, which enables hi-res audio formats like Dolby Atmos.

You may see this support article to learn more about getting Dolby Atmos on your Sonos Arc.

If you have any questions,  feel free to reach out.

Keep the TV set to passthrough. Dolby Atmos via Dolby Digital Plus is what you should be getting from Netflix.

@Ggnore Netflix (and other streaming services) only carry the lossy form of Dolby Atmos via Dolby Digital Plus. There is too much audio data to stream the lossless form of Dolby Atmos through streaming services. If you want lossless Dolby Atmos via Dolby TrueHD, you need to get a Blu-ray player.

With the Auto setting, I think your TV might be detecting the highest quality audio the Sonos Arc can output and converting whatever audio signal it receives up to a “Dolby Atmos” signal even though it may or may not actually be Dolby Atmos. TCLs with Roku TV and newer Roku Ultras do a similar conversion. Just set your LG TV to Passthrough and you are good to go.

Is Sonos ever going to chime in here?

I’ve been searching for this specific thread and I’m grateful to find it.

I have the same question plus another related one: I also have the LG CX and when I set audio settings Digital Sound Out to “Auto” on the HDMI input connected to my Apple TV, I get Dolby Atmos detected on the Sonos app.

This is the rub, though. I have the eArc setting on this HDMI input set to “On.” It’s also on for the actual eArc HDMI input. So it’s effectively on twice (I think).

If I turn the eArc to “Off” on the HDMI input connected to the Apple TV and set it to pass through, I get Dolby Atmos (DD +) on the Sonos app. If I attempt passthrough with the eArc mode on the HDMI connected to the Apple TV to “On,” it reverses all the existing picture settings such as motion smoothing, which turns on for some reason even though it’s an audio setting.

A bit confusing, I realize. I’ve been confounded by this for two weeks.

But based on what I’m reading above, for Apple TV streaming content, it should be displayed as Dolby Atmos DD +. Ergo, the eArc should be turned off the for input connected to the Apple TV and only the actual eArc HDMI port should be set to “On.”

Any advice or confirmation on this would be greatly appreciated.

@GuitarSuperstar I’ve been playing mostly Atmos content via apps, but any other format is appearing properly in the Sonos app when the TV audio setting is set to “Auto.” I was testing a Netflix program earlier via ATV4K and it displayed as Dolby Digital 5.1 PCM. So it’s not just outputting all content as Atmos.

I continued to deep dive after posting and, while most recommendations are to set the TV audio at passthrough, “Auto” is the only one that appears to work properly for me. I’ve tried every permutation and passing through audio on the TV from the ATV4K not only loses the full Atmos label, it won’t display Dolby Vision in this state. Which makes no sense, but the TV goes black momentarily, refreshes and the Dolby Vision label will no longer appear when audio “passthrough” is selected..

Needless to say I prefer both of these to be active.

I thank you for the feedback. This has been quite a puzzle to solve.

@Ggnore Dolby Digital Plus is what you want to be getting from Prime Video.