Whew, a fairly recent topic.
I had a few thoughts on this, and my thoughts are pretty much just like plenum's.
Add in a bunch of "placeholder" coding for sounds. Allow people to add in their own sounds for certain events. Certain announcements or special announcements can get their own signals if they're important enough. Ordinary tasks right now would be unimportant and too tedious to add in (like hauling and treecutting and mining and would quickly overlap each other). Basic stuff, like:
- Death (for struck down, bleed to death, suffocate)
- Cave-in
- All "Spoiler"/Artifact/Siege/Migrant/Trader announcements
- Ambiance (for the big stuff only - giant eagles, elephants, etc)
- "Strike with weapon" sounds that would play in fairly common (not every attack) for battles for slicing, bludgeoning, and piercing weapons, and maybe wrestling
- Any other events that should grab the player's attention
Ordinary dorfing tasks don't need sounds for 'em, but audio stimulation for things that should grab the player's attention would be good. The more the merrier, and the player can always remove files from the audio directory if they don't like audio cues for a specific event.
For dulling sounds that are distant how about an imaginary marker in the center of the screen. Anything within XX tiles in a circular pattern on the current z-level of it is full blown normal audio. Anything past that to a limit of YY tiles is "softened", and anything past that is omitted. Optionally, sounds up or down one z-level that are separated by rock, the sounds can be "muffled" if they're inside the XX limit. Anything from XX to YY would be "softened" and "muffled" (read: inaudible) for a little more ease of locating the source. The one problem would be that unless DF modifies the sound files in-game, players would have to go into their favorite editor and make 2-3 versions of each file. By comparison, it wouldn't be too many files and would probably be much less work compared to coding the game to change the audio itself.
Of course all in all that system's probably a little way more complex than what DF would need.