You simply must see this video and read the article.
This is sooo important. Getting the sound to sound right.
The thing I was most surprised about was that CDs are 5 times better then the best quality MP3s!
I hear the CD DJs going: "Aaaah... So that's why you shouldn't use computers!". But most of the CD DJs I know normaly burn their CDs them selves from purchased MP3s, so there is not much to gain from that.
Take note! It's better to buy high quality tracks from sites like Beat Port, but you are not guarrantied that the tracks will be mastered properly. However... They will sound better.
It's a tough world to live in.
and even more