Spawn object, or not, depending on audio properties

Hello guys. I started working on a rhythm game. You know, there are a few lanes, and "discs" are going along them, and you have to press correct key just before the object goes out of the lane.

And now I have a problem. I did almost all basic scripting, except one thing. Is there any way to, for example, depending on volume/other property when the sound object will spawn? I hope you know what I mean. And this remainds me another thing. Is there any way to make something like local files scanning, and letting player select song from his own device (local storage)? If so, how to do it, and on which platforms it works? I appreciate any help, thanks guys ;)