• Tap a placed note to open its menu — lock it there, shape it, or move it.
• Press space to dial in a note's sound before placing it.
• Press and drag before releasing to make a note bigger and louder.
• The little spinning discs are synchroscopes. Where two notes' overtones almost meet, they throb against each other — the disc turns once per throb and stands still when they lock. A shaking line is turbulence: overtones too close to fuse, too far apart to throb.
• north picks the tuning. magnetic is the piano's: close to pure everywhere, exact nowhere. true tunes each chord to pure ratios, so it stops beating inside itself — but not with its neighbours. No tuning settles everything at once.
• Pure notes are single sine waves with no overtones to collide. Give a note a resonant, nasal or cold timbre to hear its overtones at work.
• autopilot takes the controls. drift sets every note wandering. flight tunes it to live air traffic over a real airport — each aircraft becomes a note, rising through the registers as it climbs.

For the theory and the mathematics, there is a paper.

“As artists we don’t finish it: we start it. It goes on to have a life without us, a life we didn’t predict.” Brian Eno & Bette Adriaanse, What Art Does: An Unfinished Theory