You would need audio editing software for that. I have the paid version of GoldWave, which is incredibly versatile for a home-user audio processing program. The two things I use it for most frequently is to standardize the volume of all of my mp3s and to remove tape hiss from older recordings. ("Black Dog" by Led Zeppelin never sounded so good as when it's been run through a light hiss removal filter.) You can get a trial version that will let you perform 1,000 (or is it 2,000?) commands for free.
ETA: Oh yeah, I also used it to make bumper music for a friend of mine who had a radio show years ago.
Last edited by Drover; 11-21-2010 at 10:29 PM..