apple tv 4k theater set up: arc ultra era 300’s gen 3 sub

If you were playing through Apple TV with the output set to the HDMI-ARC output on the TV, then the bolded is impossible.  The “Ambient” and “Full” settings for surrounds are for audio sources only (meaning sources not coming from the TV via HDMI-ARC).  It doesn’t have any effect on HDMI-ARC sources. 

You may have had the Apple TV outputting to Airplay, but that is not the recommended setting for TV sources or Atmos Audio, because it only puts out stereo.  No DD 5.1, no DD+ and no Atmos from TV (HDMI-ARC) or Atmos Audio through the Sonos app.  So I don’t know what you were hearing before, but it wasn’t Atmos if the source responded to “Ambient” and “Full” in the Sonos app.

​@Tysoncrosbie 

jgatie is 100% correct. The Ambient/Full setting does not apply to TV (hdmi) input. What you may have been hearing is an ambient sound in the surrounds that sonos generates when the TV is sending a stereo signal. So, the question becomes, why aren’t your hearing it now?

A few months back, Apple introduced a new audio feature with tvOS 26.4 that was turned on by default. It is located in the AppleTV audio settings under Audio Format and is called Continuous Audio Connection. CAC for short.

Before that settings existed or was turned on, the audio output formats from the AppleTV 4K were (as shown in Sonos controller):
“Stereo PCM” for stereo
“Multichannel PCM 5.1” for 5.1 etc
“Dolby Atmos” for Dolby MAT (which Apple sends Atmos in)

With the new setting turned on, all audio is sent in Dolby MAT, which sonos displays as Dolby Atmos.

Sonos uses the Stereo PCM input when generating the ambient sound in the surrounds for stereo input.

If you turn off the new Continuous Audio Connection setting in the AppleTV 4K, it goes back to the way it was before.

I just tested this on my setup* to make sure nothing changed since the last time I tested it. When CAC is on and AppleTV 4K is outputting stereo, I hear nothing in the surrounds. When CAC is off and the AppleTV 4K is outputting stereo, I hear the ambient sound sonos generates for the surrounds.

You can test this yourself and see if that is what you were previously hearing. Turn CAC off and play stereo music in Apple Music on the AppleTV 4K. Do you hear anything in the surrounds?

*Beam 2, Sub (Gen 3), Era 100s surrounds

Sonos does not require factory resets outside a few rare situations, Sonos even recommends against them until you have consulted support.

A factory reset rarely solves a problem, it may hide it for a time but it is still there. It does destroy valuable, to Sonos support, data making troubleshooting more difficult.

Okay. I did not factory reset and I tested all the options on my tv and the Apple TV device. 

none of it resulted in surrounds working like I remembered before. 

I think before I was able to set it as bypass and bitstream which resulted in the music app working like I remember but with the introduction of the continuous setting on Apple TV it either sends stereo or a format that Sonos can’t convert  

it works as I expect it to through AirPlay full/ambient atmos etc. (meaning it /can/ work but now it’s either pcm stereo or nothing through the Apple TV music app. 

my original point stands it’s pretty unacceptable that I can’t set speakers up how I want but have to instead select specific sources or apps for different results. 

the continuous setting on Apple TV does sends data and shows it as Dolby atmos. But there is no way to access the “Spatial Audio” when played through my tv which by all settings isn’t touching the format between the Apple TV and Sonos  

if atmos for tv works for all other content but doesn’t work for the music app?? 

and as referenced in this thread the indecision between audiophiles and general users by Sonos seems to be at the heart of this. If it’s not just plain cooperate gamesmanship about platfom user numbers. 

When I play an Atmos track using Apple Music on the Apple TV device, it plays as Atmos on Sonos. Turn CAC off so you can see the actual format in Sonos. Because with CAC on, all audio is sent Dolby MAT which Sonos displays as Dolby Atmos, whether is is Atmos or not. In which case you can’t see what the actual audio format is.

I just tested this with the album RPWL - World Through My Eyes (Revisited) - 20th Anniversary Version.

Make sure in the Apple TV settings → Apps → Music → Dolby Atmos = Automatic.

The crux of this solution is changing my settings in my tv (lg oled g4) ::

When I disable I get pcm stereo for music and movies and since it’s my theater that’s a big compromise. 

I don’t know what else to suggest. Atmos music on Apple TV’s Music app does work. Maybe your TV settings?  I don’t have an LG, so can’t help you there.