On compression...Attack, Release, Ratio's, what compression was actually doing and when it should be used.
The mixing stage is far far more important than the mastering stage and a treated environment with good monitors with a flat frequency response to guide your mixing choices is essential for consistent results and an environment that tells you what you need to hear, not what you want to hear.
But like
@Iron Keys said, mix engineering is its own profession and art, separate from music composition theory, with a few crossovers but not really that many. You can go your whole life and not waste time to learn mixing when you could be knocking out beats, then paying a professional to do it for you.
Personally, Ive always been a broke ass, so I learned it so I wouldn't have to pay somebody else to do it, but Im certainly no expert and when the time comes and Im making some decent money from my catalogue, then I will invest in professionals for the best results.
I wanted to make music, I learned it, I wanted to build a website, I learned it, I wanted to mix, I learned it. I dont have an environment to master, but Id like to add that to my skillset at some point, when I have the equipment and space to do it. Im a fairly intelligent guy, or so my peers tell me, Im capable of learning these things, not everybody is. Its about knowing yourself and your own strengths and weakness and either working on those weaknesses, or paying somebody that already has.
