the indigenous orchestra type of Java and Bali, consisting largely of several varieties of gongs and various sets of tuned metal instruments that are struck with mallets. The gongs are either suspended vertically or, as with the knobbed-centre, kettle-shaped bonang, placed flat. Percussive melodic instruments include sets of tuned bonangs, xylophones (the gambang kayu), and metallophones (these are instruments with a series of tuned metal plates, either suspended over a resonance trough or on resonance tubes). A sustained melody is played either by the bamboo flute (the suling) or by a bowed string instrument (rebab (kamanjā)) or is sung—the last especially when, as often occurs, the gamelan is used to accompany theatrical performances, or wayangs (wayang). The voice is then part of the orchestral texture. Dominating these two groups of instruments is the drum (the kendang), which unites them and acts as leader. Javanese gamelans frequently include singers, while Balinese gamelans consist exclusively of percussion instruments. Many types of gamelans, of different sizes and for a variety of purposes, may be distinguished.

No two gamelans are precisely alike tonally, for each instrument is tuned only to the gamelan for which it is intended rather than to an external standard of pitch. A gamelan typically consists of two sets of instruments, one tuned to the scale of slendro (in which the octave is divided into five tones roughly equidistant) and the other to pelog (a scale consisting of seven notes of varying intervals of which five are given principal stress). The modes (patet) of gamelan music are determined by the relative placement on either scale of the basic note (dong) and its fifth above and fifth below. (A fifth is an interval more or less the size of that formed by five adjacent white keys on a piano.)

The highly developed polyphony (multipart music) or heterophony (music in which one part varies a melody played simultaneously in another part) of the gamelan has a rhythmic origin. A nuclear theme extends over a number of “bars” (almost invariably in ⁴/₄ time), against which other instruments play a largely independent countermelody. Another group plays rhythmic paraphrases of this theme, and a fourth group fills out the texture with delicate rhythmic patterns. Highly important are the punctuating, or colotomic (colotomic structure), instruments that divide the musical sentence, marking, as it were, the commas, semicolons, and periods. This last-named function is done with the big gong. Over this shimmering, variegated pattern of hammered sound floats the uninterrupted melodic line of the voice, the flute, or the rebab.