I just got Soundbooth CS5 for my iMac yesterday. I plugged a standard dynamic microphone into the mic input in the back using an XLR to 1/8 inch cable. But I can't get the mic to pick up levels in Soundbooth. It will only pick up the built in mic. I'm relatively new to tinkering with these things so how do I get Soundbooth to pick up my mic?