it writes in circles
20 HP
An oscillator you can hit. A ring of masses ripples at the speed of your hand while a head reads it at the note you ask for, so the ring's shape is the wave, and the stroke of light round PITCH is the ring. Strike it, rub it, hold it still.
Turn a knob: drag it or tap either side of it, roll the wheel over it or use the arrow keys; a double click puts it back. Touch the ring: tap it to strike it there; press and stay to hold it still; drag round it and it pushes, and at the ripple's own speed it builds. Or tab to it, move along it with the arrow keys and hold Enter or Space. The patches step on by themselves until you touch anything.
example patches
The ring, the head and everything they do are LOGOGRAM's engine as designed, running in your browser, on a model of a ring of masses. What plays into it stands in for a rack.
One board 10 mm behind the panel, every part on its front. Round PITCH, 108 white LEDs, one in each cell of a printed white frame; its row walls have black cores, so the hairline stays one. The panel is a circuit board too: the ring's 24 touch sectors are copper just under its face, read by two chips on its back.
Drag it or use the arrow keys to turn it; click it to take it apart.