Harmonograph

A harmonograph is a Victorian drawing machine: pendulums swing a pen across paper, and as they slow down they draw spiralling figures. Here one pendulum moves the pen left and right and another moves it up and down. Each pendulum is also a note, and the ratio between their speeds is the musical interval.

A fifth is 3:2, so one pendulum swings three times while the other swings twice. That ratio sets the pitches, the shape of the figure, and the rhythm of the bells. Each pendulum rings softly as it passes through the middle, and rings its fifth and octave at the two ends of its swing.

• Just tuning uses pure ratios, so the figure closes on itself
• Equal tuning uses the piano’s rounded ratios, so the figure slowly turns
• Drift nudges the ratio off, and the turning you see is the beating you hear
• Tempo sets the slow pendulum to one swing per bar, so its bells fall on the beats and the other pendulum plays the ratio against them (a fifth is 3 against 2)
• Play it like Polyrhythm: hold a key (Z to M, plus S D G H J for sharps) or the on-screen piano to move the root, and the swing holds while you do. 1 to 6 change the interval on the next beat
• Settings ease in mid-swing, so the figure morphs instead of starting over
• Damping sets how long a swing lasts, Auto picks a new interval when one fades

Changelog

• Initial release