Each note is a clapper strike convolved with an impulse response synthesised for that exact note: one and a half to twelve milliseconds of low-passed noise with a leading tick, driving a bank of exponentially-decaying sinusoids placed at the selected family's measured partial ratios. Convolving the strike with those modes is what excites them, which is why the Clapper control changes the balance of partials rather than only the brightness, a wider excitation spectrum reaches further up the bank.
The five datasets are the module. A carillon gets ten partials with the founder's five tuned ones at the bottom (0.5, 1, 1.2, 1.5, 2) and a hum whose decay is the slowest in the bank, so it outlasts everything above it. A tubular bell gets the thin-tube series normalised so that ratio 1.0 is the virtual strike note an octave below its fourth mode. A handbell gets four partials with the twelfth on top of the fundamental. Glass gets a near-harmonic series with a small stiffness stretch and very fast upper decays. A bowl gets three shell modes, each split into a doublet a fraction of a percent apart so the halves beat against each other in both channels.
Strike position is applied to the modes before the impulse response is rendered, so it changes which partials exist rather than filtering the ones that do. Two lobes are blended across the bank: at the soundbow the low partials are full and the top of the bank sits at about a third of its weight, and up the waist that inverts. Nothing is ever weighted to zero, because a clapper has width and never lands on a mathematical point, a bell struck off its soundbow is thinner, not absent.
Casting size is applied to the partial ratios about the played pitch rather than about the lowest mode in the bank. That distinction is load-bearing here in a way it is not for the sibling instruments: a carillon's lowest mode is the hum, half an octave below the note, so pivoting there would drag the prime, and therefore the pitch you hear, every time the knob moved. Pivoting on the note itself leaves the pitch immovable at every size and lets only the inharmonicity breathe, which is the real difference between a small bell and a large one.
Velocity does two things, both physical. Level follows velocity squared, the repo's own perceptual curve. And a harder swing is a shorter contact, which is a wider excitation spectrum, so velocity is coupled into the clapper's effective hardness, a quiet strike is genuinely duller and not merely quieter. There is no knob to defeat that coupling, because a clapper cannot be chosen independently of the stroke that swings it. The exciter burst is drawn from a seeded generator forked by the clapper setting, so a given touch always produces the same burst; Math.random has no place in this path.
Rendering an impulse response is millions of sine evaluations, so they are cached per family and note and dropped wholesale whenever a parameter that changes the samples moves, family, ring, damping, casting, width or position. Voices are capped at eight with oldest-first stealing, and a voice's nodes are freed on a nine-second tail cap with a short fade, or as soon as a note-off's release has run, whichever comes first. Tuning is twelve-tone equal temperament with A4 at 440 and nothing else: a founder casts to concert pitch, and every key on the keyboard has a bell behind it.
