odd question, but when do you know you're "good" at mixing and mastering? also, thx for your articles on your web site, they're great!
Thank you! If people like what you're doing, this means that you're good at what you do. Especially if it's people who are just fans of the music and not engineers; most of the time other engineers forget about just listening to music and automatically like to pick it apart technically, so don't pay attention to what another engineer thinks of your work. From the point of view of a music fan, if what you're doing sounds pleasing and people listen to what you've worked on a lot, and your work doesn't hurt the ears from over-processing, to me that's a sign of a good engineer!

