Modal synthesis
A struck bar rings at a few fixed frequencies. Add them up and you have a marimba.
Strike a metal bar or a wine glass and it rings — but not at one clean pitch. It vibrates at a handful of specific frequencies at once, its modes, and those frequencies usually are not neat multiples of each other. Modal synthesis recreates that by adding up just those few partials.
Each material above rings at different mode ratios. A wooden marimba bar's overtones sit near 1 : 3.9 : 9.2 — jangly and inharmonic — and die away fast. A metal vibraphone bar rings at cleaner ratios for much longer. There is no filter here: the choice of partials, and how fast each one decays, is the entire instrument — which is why modal synthesis is perfect for mallets, bells and chimes.
It is a close cousin of additive synthesis — both build a sound from sine partials — but modal uses only a few, inharmonic ones, each with its own envelope.