Gamelan

The struck key’s octave of the instrument: pélog’s seven bars over sléndro’s five (or twelve in a row), over their tubes on a gangsa, or the kettles and gongs with their bosses. Each glows as it rings; a pair’s two partners swell and fade together at the beat.

Left: the two partners’ notes as arrows, turning against each other at the beat; their sum, what you hear, swells when they line up and vanishes when they oppose. Right: the struck key’s level over the last three seconds, the beat riding on its decay.

A bar’s first bending modes along its length and its first twisting mode, and where the mallet lands (dashed): on a node a mode stays silent. A gong’s modes from above, their nodal circles and diameters, the boss at the centre and the beater’s spot.

A bar’s overtones at about 2.7 and 5.2 × the note, none of them harmonic; struck off its axis, its twisting modes between. A gong’s note stands alone at the bottom, its second harmonic (made by the face’s curvature) just above its second round mode.

The overtones die within a second and the note hums on. A pair’s note pulses at the beat; a gong ageng’s line near twice its note throbs slowly, its own ombak.