Hey, if water bodies get their own music, why shouldn't caves and mines? You can potentially spend a lot of time in them to the point they're they're own world/dimension as well. I get the creepy aspect in wanting to make them quieter, but it's also really odd hearing Overworld Survival/Creative music play in the midst of ambiance, bat squeaks, and other underground stuff.
EDIT: How about the Nether's smaller caves too, while we're at it? (Okay, that seems less necessary. But give it a thought).
The issue is MC kinda has little idea what actual situation are you in. Are you in a dark scary cave, a massive majestic ravine or in a perfectly lit comfy underground base? Even overworld, it seems to have little distinction between being in your lit and fortified home area, or out in the wilds chased by mobs.
I suppose some biome-specific musics would be cool. Altitude dependent music too. If you are at cloud level or above, chances are you got a spectacular view.
As it has been stated before, MC doesn't have idea where you are. And to be honest, if there even is some decent algorithm to determine that, you'd probably need proper beast of a computer. Because:
Are you in your home area? How do you define that? For me it's simple, granitum imperial walls. for others? I have no idea.
If you're at your home, where are you? Because I can be at my vertical farm, on construction of another building complex or in collection room fo Dark rooms. Or maybe in some dark room itself, if I feel like it. How MC should know, what is cave and what isn't? Because my construction site doesn't have much light, because I cannot put it there yet, because it's not built yet. And I might be at y=74, under some ceiling of lateres saxei and above them is just dirt and water, because my farm needed expanding. How MC should know…any of this? It's in my empire, yet there is dark, but not everywhere, there are mobs spawning, and I don't really care about them (unless they care about me).
It¨s just so complicated, so difficult. And for…what? Music? I'm sorry, but no. If it would be for something proper, then sure.
Well, music in a game can really alter the experience. A visit to Plane of Torment in Everquest was quite a trip with it spiky walkways slowly appearing out of red fog, but what really put it together was music.
Lord of the Rings Online has a darn good score for many if its areas.
And if you ever played Deus Ex Human Revolution, when you first set foot in Tai Yong Medical penthouse is just... special.
ya know how they can do this? this already implemented thing called regional difficulty. the longer your in an area, the less ambient music is played. (im not saying that is what regional difficulty does, but it is a similar concept)
Here are some things that could help define music to the programming which are already in place:
A) Boss bars - play music when they're on-screen, and different music based on whether they're charging (reviving dragon, growing wither, inciting raid) or you're actually fighting. You can even have the music speed inversely correlated to the health left of the boss, as such that it gets frantic as they get more hurt, and if they recharge via crystal or natural healing, it slows down. For raids, the wave concept also allows additional changes - such as another instrument joining the music with each wave to build up the fight.
Non-boss Hostile mob detects you - if a hostile mob sees you or a neutral mob gets angry at you, and your regional difficulty is below a level (or above a level), quiet and short tracks play to warn you or to jazz up the fight. NOTE:Except for creepers! They should have a very quiet soundtrack or none at all! These can go with the ambient scene music tracks and the cave sounds just fine. The game can also easily tell how many mobs are after you - maybe the music is louder or sharper when there are 4+, and screaming if you have a whole village after you (e.g. zombie villages, ocean ruins).
C) A short sad piece (under 10 seconds) can have a chance to play if a villager, golem, stray cat, neutral witch, or tamed animal dies near the player.
D) Seeing diamond ore for the first time could make a jingle or triumphant trumpet sound play. This works programmatically because the F3 screen shows the game knows what block you're looking at (in order to direct mining time if you try hit it). EDIT: How about bone blocks as well, for fossils?
E) Man-made structures are defined in the world even if every block in them is removed. This is proven true at least for villages (by the raid boss-bar), monuments (where the elder guardians can target you with mining fatigue spells) and for structures that give you advancements upon entry (fortresses, cities, strongholds, mansions and monuments in Bedrock and PE). I imagine mine-shafts are still defined since in older versions they would spawn dark in super-flat worlds if they were above-ground, indicating their light is independent and thus they are solid. So the only really maze-y, multi-level structures for which this might not work are zombie villages (no doors) and ocean ruins (no proof of underlying structural frame). But then could cover these since they have swarms of un-dead, and igloo basements and swamp huts can similarly be covered by because of witches and zombie clerics. Then, music only plays in pyramids if there are actual mobs.
F) When near an active spawner. This could help with E) in case mine-shafts are not implicitly defined so at least you have suspense for cave spiders, and they would also take care of dungeons. However, maybe the music only plays after the first batch of mobs is made. This may be a problem for mansions as it would reveal the location of secret spider nests in upper floors almost right away, in case all the mob sounds don't warn you.
G) By far the hardest to manage, caves and holes in the land of all types. For one, caves with some sunlight and rock basins and rock shields on the surface shouldn't have music. Sunlight can be detected since F3 shows it is distinct from block light, and even at night this applies. However, it's not at all clear whether caves themselves are defined structures! A few possibilities include playing whole soundtracks when near dark areas, dark water, or lots of lava, or even bats, but these would overlap when in structures and with existing cave ambiance and ocean ambiance, not to mention all the lava in the nether and all the darkness both there and in the End. So this would have to be overworld only, not in oceans, and between elevations 12-63 (below ground, above lava). Many potential issues getting this to work.
And even all this aside, who would make all this music? C4-18 can't just make like 3 dozen tracks all at once, even if they're short and some repeat uses. And to make this addition interesting, each structure, boss fight, and most mobs should have distinct music.
In addition, this is overall not that good an idea because part of what makes Minecraft scary is that you get attacked by mobs and spooked by things in the dark because there is no music to warn you. It's like why old Slenderman YouTube series were scary; no warning music for when assailants arrived. So the only reasons this should go through are a) to make the game more adventure-y and because overworld music sounds weird when spelunking in darkness. Maybe there could be a toggle on-off switch for extra music, but many people say optional experiences like that ruin gameplay, you don't pick and choose what you want in most games.