Audio database is recorded under * conditions

Such circumstances are usually called real-world conditions (i.e. - not controlled conditions).

Only my own opinion, but personally I think OP's suggested "realistic conditions" implies controlled, artificial conditions - although specifically designed to mimic real-world conditions, there's always a chance the testers either failed to set things up as they intended, or were unaware of some crucial aspect of the "real real" world.

You might say under existing conditions, or imperfect, uncontrolled, run of the mill, flawed, as-found, ordinary, mediocre. Cornbread ninja's suggestion of everyday also is good, and its definition leads to commonplace (as well as ordinary, already suggested).

I have often heard the background sounds referred to as the ambient noise.

What is Ambient Noise?

"Ambient conditions" seems to have more use on the Web as referring to weather, but if you told me that whatever I was about to listen to was recorded under ambient conditons I would be expecting background noise.