Knowing how to "hear" is a big help. It's also very hard to "teach" mastering, since it is, in my opinion, very "feel" oriented.
It used to also be a fidelity related trade, now, not so much. If you have the latest "clipper", "squeezer", "smasher" in your plug-in box, you can master. .
Typical mastering session are now no longer how GOOD we can make music sound, it's how LOUD we can make it sound, as if THAT sells one more CD or download.
The typical condition that mixes arrive at mastering, anyway these days, there is really little that can be done anyway, as most everyone mixes thru mastering tools, and most material is so destroyec/mangled beyond all hope, that mastering is usually nothing more than squeeze it some more, beat the balance of any life that's left in it.
My favorite comment though is "Boy it really sounds great, lots of dynamics, but can you make it about 6 db louder and keep all those dynamics and impact?" Then it's the long explanation about maximum level, and all that stuff.
Many times now, I'm glad I DON'T work in the mainstream arena. There's got to be very little satisfaction with what gets turned out now for commercial release. Where I am now, I get to set the basic tone and volume for our products, and since we're basically a catalog group, we don't get saddled with playing the "level game", and those few front line products, the artists become aware of the problems with the typical smash/burn approach.
Couldn't agree more. What happened to it's about the music. Now it's about the volume.
Music doesn't move anymore. But I try my best to throw a rock into that still water and ripple things up a bit.
A new set of ears is just one aspect. In a lot of cases it should be refered to as a fresh set of ears. I find that when I work on a production from start to finish, I get wrapped up in certain areas of the production. Sometimes it is that fresh set of ears that can help keep you on the right path.
As far as the rest, ears and experience. But you have and know that.
I think a great mastering engineer is someone who can create more clarity and enhance the punch if it needs it so you can feel it in your chest when their done with it. (not castrate it by overcompression) Someone who cares about their work and pays attention to details. I think they have to actually loves music and be happy mastering records! (not necessarily a given) I think that lots of experience is important - a great mastering engineer has to screw up his share of records before they can do it well.