I'll give you my semi-informed answer, but I'm also gonna reach out to a friend who has worked for Dolby for decades and see if he can give an even more informed answer. But the basics are that while most music is mixed for 2 channel stereo, and some is mixed for 5.1, Atmos is at minimum a 7.1.4 format, meaning left, center, right, left surround, right surround, left rear surround, right rear surround, subwoofer, left and right front overhead speakers and left and right rear overhead speakers (Atmos supports more than that, so the 21 speakers in the Lucid may get extra audio depending on how the Dolby codec works with the Lucid DSP/Amps).
The audio engineer aka mixer decides which sound goes where when it's mixed or remixed for atmos. The Dolby Atmos mixing software also allows you to create beds and objects, where beds are evenly allocated to the appropriate speaker assignments in 3D space, and objects can be discreetly moved from one speaker to another. Prince's When Doves Cry Atmos mix is the perfect example of the synths being used as a forward biased bed, while the effects on the synths (reverb and flange) are split to the rear speakers as a rear biased bed, and the guitar in the beginning is an object that is discreetly flung from speaker to speaker all around the car/room. Meanwhile his background stacked vocals are split left and right while the primary vocal is dead center and I think even sometimes in the front overheads so it sounds like he is right in front of your face. This mix is locked into the Dolby codec and so you can't change position or balance (why would anyone want to haha), as it was already pre-defined and encoded. But yeah you can change the EQ in an admittedly limited way because EQ doesn't affect sonic position.
Another great example of how you can use Atmos is on
@hydbob Lucid Atmos Test Tidal playlist, playing the Atmos track La Vie En Rose by Madeline Peyroux. For this song it wouldn't make sense to do flying around the room trickery like the Prince track, instead what they did is place each instrument in its own spatial location on stage with the vocals in the middle so if you close your eyes it sounds like you are
right there listening to it live in person. It's funny because to me, I've never heard a more realistic natural sounding presentation of recorded audio, and it's taken almost 100 years of audio recording technology to get to the point where you can actually recreate sonic realism. I even heard an early demo of direct stream digital through top tier audiophile equipment at an Audio Engineer Society conference in NYC years ago, and I thought that sounded pretty realistic, but what I've heard on the Atmos system in the Lucid, well the Lucid beats it.
Atmos in cars creates an interesting dilemma though, as up until the Lucid, car audio was the wild west and utterly non-standardized, and tastes got defined by car audio manufacturers who would do all sorts of cool things that would hype different frequencies and make up for the deficiencies of what is really an absolutely shit listening environment, with glass and weird reflecting and absorbing surfaces and engine noise and road noise etc. I think up until I heard the Lucid I'd say Burmester was the best at car audio, with things sounding musical but pretty accurate. But now you have the Lucid which is quiet and carefully tuned and mostly non-modifiable because to play back any Dolby audio you can't modify it, and people say it sounds bad even though it's likely the most accurate representation of how it sounded in the studio. Sorry for the very long post, but I guess these are interesting times in which we live and sometimes require too many words...
