As a non-musician, I use a wonderful editor called
CoolEdit Pro 2.1 (Now called Adobe Audition). It has a drop dead easy to understand interface (which is just my speed, lol) and the enhancements you can make to files is awesome. Just recently I converted an old Mono file of Ultraviolet's into a supercharged stereo rendition that is dripping with atmospherics.
I didn't add or subtract anything, but just enhanced the various sections using a number of filters.
The reason I got into sound editing was because in the early days of Napster, many songs came with annoying flaws, superfluous radio intro's and exits, and wild balance levels. I think CoolEdit was worth its weight in solid gold simply by giving the user the ability to edit an MP3, normalize the sound levels and resave it as an MP3. Though MP3 is a losy process, you can actually work with an MP3 file that is poor to begin with, clean it up and come out with a better product than you downloaded.