normally, you'd normalize each track so that they're all at the loudest they can be, but since you've recorded this as a mix, I'm assuming they're 1 contiguous track, not seperate choons, right?
If so, you could go and select just the song part you want and normalize that, but you'll end up with jumpy volume levels between the mix part and the main part
That's about the only way I can think of doing it...anyone else? I don't usually meddle with my mixes in the computer...too much hassle
