Does anyone know how ambient sounds work in the Sims 3? Namely, what influences them?

Eg.
- A wave effect creates a shoreline sound.
- A seagull effect creates a seagull sound.
- What would make the city sounds that you hear in downtown Bridgeport?
- What would make the cicada sounds?
- What other triggers/sound combinations are possible?

Thanks

Buzzler have some sound balls in the builders mad hatter mod. I haven't seen it in the catalogue with the mod though, and don't know how it works. Should have something to do with highrises ...