Plays a song's loops together, each in its own process, against one shared beat.

The band keeps the tempo timeline, as Mx.Tempo describes it. Every loop works out the real time of its notes from that timeline, so loops of any length keep their place against the same beat. A saved version with a new tempo starts it on the first whole beat after the notes already sent, so every loop changes on that beat. The tempo changes a song's music writes go on the timeline when the first loop cues the pass they are in, before any loop sends a note of that pass.

When the song changes, a changed loop takes over at the end of its own pass, a new loop starts on the next beat, and a removed loop stops at the end of its pass, unless it is added back before then, when it takes over at that end as a changed loop does. The band starts a loop again when its process fails. Given subscribe, it subscribes to the inputs, and passes each one to the loops whose on: waits for it. Each version's live audio goes to live, which starts, changes and stops it. Each version of the song goes through prepare first, which loads its samples, so playing starts only once they are ready. When every loop has played its last pass, the band calls on_end. Given from, a beat of the song, each loop starts in the pass that holds that beat and plays it from there, so that beat sounds first; a loop whose passes end before it does not start. A part a new version of a song written as music adds joins at the next section, with the pass number the other parts play there. Every loop with a start beat is handed to worked_out with that beat before any loop works out a pass, so no loop's pass reads the shared values before the other loops' set steps are in.