Key Transition

A tool for arranging DJ sets. Give it the key you are in and the key you want to reach, and it finds the shortest sequence of mixes that gets there without a clash, working around the Camelot wheel.

The wheel is modelled as a graph of twelve positions in minor and major, with an edge for every move harmonic mixing allows — a step either way around the wheel, or a switch between relative minor and major. A breadth-first search over that graph gives the shortest route, and enumerating the longer ones produces a collapsible list of alternatives up to two mixes further: the shortest path is not much use when it runs through a key you own no tracks in. Keys can be read as either notation, so Ebm to A and 1A to 8B are one click apart.