As far as I’m aware, the Full/ambient setting is only in effect when the surround speakers are receiving surround data from the ARC or optical line in on the home theater ‘front’ device. That setting would not be in use when there is any WiFi streaming going on. 

I think I said that backwards…and not easily understood. My sincere apologies.

The Full/Ambient switch is only in use when WiFi streaming is in effect, via the Sonos Controller, AirPlay 2, or Bluetooth, to the ‘front’ device of the Sonos ‘Room’

That switch is ignored when the digital input is used (either an optical on older devices, or ARC on newer devices).

Hopefully, that makes more sense. 

All audio coming via ARC or Optical is treated as TV audio.

The Full/Ambient options are specifically for Music playback which is stated in the app.

I ‘want’ to separate those as inputs, rather than TV, but yes, you’re right. 

​@bogdalene - Are you definitely streaming Dolby Atmos music at the time when you switch between the options? Do you see the Dolby Atmos badge in the Sonos app for the track playing?

​@Airgetlam yeah that makes sense! but yeah unfortunately this issue is happening while listening to Atmos music through the Sonos app, which states that it shouldn’t affect Atmos.

​@Mr. T Yep 100% Atmos is coming through and the badge is there too!

I think the snip below best sums things up regarding Full/Ambient settings for music play back with Arc Ultra and surrounds. Note that when listening to music in Dolby Atmos the settings don’t apply. The sound does change (as it should) for the Era 300’s when listening to Dolby Atmos recordings vs regular stereo regardless of the settings.

I no longer use Apple Music, but when playing atmos from Amazon Music, switching between Full/Ambient has no effect on the audio. There is no “intended” setting as neither apply to atmos music playback.

Maybe another user will be able to recreate your experience with Apple Music…

​@AjTrek1 Yeah you are correct in how it should be working, but this definitely isn’t a matter of stereo vs Atmos on the Eras. It is 100% a change in the Eras sound only while playing Atmos music. The settings work as intended for stereo music, but they shouldn’t be working at all for Atmos so I’m not sure what’s going on. When switching to ‘Full’ while listening to Atmos the Eras get noticeably brighter, for example.

​@Mr. T gotcha thank you for trying it out! I hope it’s a bug with the implementation of Apple Music and not something exclusive to my system. If I can get a trial I may test with Amazon to see if there’s any change. 

Since we don’t know what you are hearing your best next step is to run a diagnostic within 10 minutes of the sound change you describe. In fact it might be advisable to run a diagnostic before it happens to establish a base-line and then perform your test with Dolby Atmos and run the second diagnostic.

Record the reference ID’s for both diagnostics but do not post them in the forum (here). Call Sonos Tech support to discuss the results.