i have a really short question about my audio interface which is a m-audio fast track pro. my question is for what is the "pad" button used?

thx Head.Banger
It's used for things that have a very high db output. You press it and it takes off 20db from the input signal so you can get clearer recordings without having to down nearly all the way.
When you are in a loud location and have a more sensitive mic, the pad will keep things under control a little more. I can see it being useful if you had a condenser mic next to a tube amp