It sounds like little more than an "expander" with possible treble enhancement to make it sound "clearer". The real way to avoid this is to avoid MP3s all together.

Over the years I have tried various companding and expansion devices and found the pumping and breathing effects to not be worth the effort.

Your mileage may vary.

Agreed, if you don't compress the music in the first place you won't need to uncompress it. Why create an unnecessary problem only to be forced to later solve it? Hard drive space is so cheap I don't see the point in compressing anything, other than one of the excellent lossless codecs. You'll fit less on your portable device but it's so easy to move things around it actually helps keep thing fresh. I have the 60 gig iPod and I have about 170 CD's using Apple Lossless compression stored on it.