Thanks, all you wrote was so useful... And I think I'll learn more useful things in this forum. Otherwise, I only have problems with mastering. I know how to set the EQ parameters of the drums, basslines, sub etc. but the final mastering is always a problem for me. Especially the compressing and the EQ on the master. I got some critique because my first musics didn't have enough sub. So I started to focus on this. I solved that, but in my new musics sometimes there aren't enough high frequencies. So I think all I have to do is learn from my mistakes and show my music to my producer frineds before I make the mastered version or 'leaving the mastering to someone else' as you said. I'll work on it!