so i know this guy, who has had his own little studio for a few years (records local bands, the local college, religious stuff, etc) and i was explaining to him that my mixes (though great sounding in my house) sound terrible in my car. he began telling me that when he gets done with a mix, he gives to the band as a demo, and tells them that if they want it to sound professional he has to send it off to [some company] to be mastered. furthermore (he tells me), even if i get a pretty good recording of my own i would need to have it sent off to be "mastered". waiting for the question? is this true? is he right? can my little software (cool edit pro) master? what is the difference between a master and a mixdown?