I have some ideas:
First of all, I really dislike mp3s as compared to higher resolution recordings. But they are what they are.
My biggest complaint is most of them sound so COMPRESSED! And, lately, I figured out the problem. --- If you record your digital masters at too loud a level, especially tipping into the red, any computer using Vista etc. that makes .wma files, or even .wav files will slightly compress them to start with. THEN, any mp3 program that I've used further compresses the sound. I'm not talking about "lossy" compression, but audible compression.
So the trick is to make sure your digital masters peak at -2db or lower. I've really experimented with this over the last week or so, and am convinced of this. The hotter you make your mixes, the more audible "pumping" of compression you're gonna hear. As opposed to analog recordings, louder is not better when it comes to mp3s. Sure, try to get your levels as hot as possible to compete with everyone else, but when your mp3s sound like sh!t, what's the point?
My 2 cents,
Ern

