I’ve experimented with key mixing recently using digital tracks (or ripped vinyl) in Rekordbox.
After 30 years of messing around with mixing tunes I couldn’t believe I’d never really sussed it before. I think I’m basically naturally tone deaf!
Key mixing is a revelation especially mixing with acapella or vocal parts of tunes. The results really can sound spectacular and are the difference between stitching together some records at the same tempo or actually making a mix that makes sense musically.
Check out the wheel system that places the keys in order: you can go from any minor key to the other minor keys to the left or right on the wheel or jump into the corresponding major key.
No idea how you naturally determine the key of a record without it being in Rekordbox though.
Apart from using your ears, of course!
I wonder if the more musically talented among us can listen to a tune and hear what key it’s in. I certainly can’t. Most of my mixing has been built on playing what just feels like the best tune to put on next. What I’ve learned from using the key chart is there are lots of tunes I never would have thought of that work brilliantly. It’s especially useful when playing across multiple genres. If you’re mainly playing house which usually seems to be Am or Em then it’s pretty easy to mix in key anyway. Or just mix on the kick drums without any melody involved. But when you’ve got two tunes of different genres flowing seamlessly because they’re in the right keys it’s pretty ace to be honest. Worth giving it a try.