The fact that the instruments of the Gamelan (orchestra) in Java are venerated as holy objects within the context of the Javanese religion is indicative of the importance of the gamelan. The crowning musical achievement of the Javanese is in bronze: the great bronze gamelan orchestra of central Java, which in its complete modern form comprises 70 to 80 instruments. With it are solo vocalists (pasindhen) and a choir (gerongan) of up to 15 members. A complete gamelan consists of two almost identical sets of instruments with some gongs and drums common to both sets; one set is tuned to the five toned slendro tonality and one is tuned to the seven-toned pelog. No two orchestras are tuned exactly alike. Mythologically, the most revered instrument of the gamelan is the great gong (gong ageng) where, it is said, the great spirit of the orchestra resides.
The music of Bali is also dominated by ensembles of gongs (called gamelan in Indonesian). Ensembles often include a few stringed instruments, bamboo flutes, and/or vocalists. Bali supports a slightly different type of gamelan gong-chime orchestra music than that of Java. Melodic elaboration in Bali is often achieved through the use of fast, interlocking patterns. The pairs of instruments that play the interlocking parts are tuned slightly off from each other, to create a shimmering sound. Gamelan clubs are common in Bali; these clubs have recast old palace instruments to make new gong sets. One such gamelan is the gong kebyar, which uses both old and new instruments.
The orchestral compositions that make up the gamelan repertoire are highly stratified, sometimes consisting of as many as 25 distinct layers of complex, mathematically structured, simultaneous variations on a given melodic skeleton called the balungan. Balinese gamelan music is based on the precise articulation of extremely fast, interlocking parts. There is very little improvisation in Balinese gamelan music.