So to try being precise is the following correct?
TODAY (ie tvOS14)
- Atmos-encoded content sent to your TV will be handled by the TV. Meaning if you have a surround system of some sort, the TV and/or surround system processor will mix the Atmos down to your 7.1.4 or 5.1 or 3.1 or whatever speakers you have, and you will get surround sound from your soundbar+whatever extra speakers
+ the Apple TV has nothing to do with this except passing through the Atmos signal to the TV/soundbar proper
+ the angular behavior (as I turn the sound turns) happens because the speakers stay still but my head turns
- Alternatively I can tell aTV to send audio to a HomePod or two. In this case the aTV does decode the Atmos, generates an appropriate spatial signal for the HomePods, and, like above, I hear spatial sound as I turn my head.
(Presumably the multiple speakers on a single HomePod allow for some sort of spatialization beyond just stereo separation?)
+ if I tell aTV to route audio to AirPods rather than HomePod, now I just get a stereo signal from aTV, all the additional spatialization content is tossed.
TOMORROW (ie tvOS15)
- signal sent to the TV is unchanged
- signal sent to HomePod(s) is unchanged (except HomePod mini now also gets to play)
- signal sent to AirPods is modified based on my head orientation. Unlike the speaker case, when I move my head, the airpods move as well. So the aTV needs additional feedback (presumably from gyros in the airpods) that I have turned 30 degrees, and it modifies the signal to match that new orientation.
Presumably, also,
+ when this starts, the system has to assume you are facing the TV, and all changes are relative to that? If you put the airpods in with your back to the TV, then start turning, by the time you're facing the TV left audio will be on your right and vice versa?
+ do the airpods gyros also track vertical angle? ie if I bend my head to look at the roof, do the airpods know I have done that? Unclear to me. The final 4 in 7.1.4 means (in theory) that your sound system is also generating "vertically differentiated" sound, not just sound from different angles in the plane. But I don't know if (current) AirPods can provide that.
+ I'm assuming the airpods track ONLY angle, not position? But this is unclear to me.
Suppose I'm in a room listening to my fancy surround-me orchestra. I rotate and hear the violins are now coming from behind, no longer my left. OK, great. I'd also expect maybe that if I walk towards the violins they get louder.
BUT supposed I am now out walking in the street listening to the same content. What do I want? I certainly don't want violin loudness tracking my movement in space! Maybe I want them tracking my head angle? But even that becomes problematic when I hit a corner and start walking north-south rather than east-west...
(This last is no longer an aTV question, now it's an Apple Music and Spatial Audio question!)