Here's the bargain music theory hands developers: take the circle of fifths — a 700-year-old chord-relationship diagram — rotate it slightly, replace the keys with numbers, and you get a tool that lets a 16-year-old DJ build a harmonic set without knowing what "fifth" means.
That tool is the Camelot wheel. It's the foundation Mixed In Key, Rekordbox, Serato, and Engine DJ all build on. And implementing the rules in your own software takes about 50 lines of code.
What the wheel does
Every musical key has a relationship to every other key. Some pairs sound great together (relative major/minor). Some clash horribly (a minor third apart). Music theory expresses these relationships in terms like "subdominant" and "tritone substitution" — useful if you're writing a fugue, useless if you're trying to mix two house tracks at 2am.
The Camelot wheel collapses all this into a clock face: 12 numbered positions, each with an A (minor) and B (major) variant. Two tracks mix harmonically if they share a position, are adjacent on the wheel, or are on the same number with different letters.
