A struck object vibrates at a set of characteristic frequencies — its modes. The same mathematical model produces wood, metal, glass, and ceramic sounds just by changing the mode frequencies and decay rates.
Strike the object
Choose a material and strike it. Each bar below shows one vibrating mode — watch how quickly the higher modes fade compared to the fundamental.
Mode energy (each bar = one vibrating mode)
Output waveform
What makes a material sound like itself
Every object has a characteristic set of resonant frequencies determined by its shape, density, and elasticity. These are its modes. Striking the object excites all modes simultaneously, but they each decay at different rates.
Mode frequency ratios determine whether the object sounds harmonic (musical) or inharmonic (percussive). A vibrating string produces modes at exact integer multiples of the fundamental (1×, 2×, 3×…). A metal bar produces modes at irrational ratios like 1, 2.76, 5.40, 8.93 — which is why a bell sounds complex and "metallic" rather than like a pure musical tone.
Decay rate is set by the material's internal damping — how much energy is converted to heat per cycle. Metal has very low damping (long ring), wood has high damping (short thud). Each mode can have a different decay rate — typically higher modes die faster, which is why the sound of a struck object becomes darker over time.
The model. Each mode is a damped sinusoid: amplitude × sin(2π × freq × t) × e^(−decay × t). Sum all the modes together and you hear the object. This is computationally simple but surprisingly realistic — the human ear is very sensitive to the mode frequency ratios and decay curves as cues for material identity.