The term gamelan refers to the ensemble of percussion instruments on which the traditional music of Java and Bali is played. Many different types of gamelan have evolved in Indonesia over more than a thousand years, but the principal gamelan traditions are those found in Bali, Central Java, and Sunda (West Java).
Gamelan types differ mainly in the choice and number of instruments used in the ensembles, in some cases the materials of which they are made, and the musical forms or structures. Elements common to most of them are the presence of gong-type instruments (both hanging and horizontal), some form of keyed melodic instrument (usually metallophones) and the frequent use of cyclic forms. Central Javanese gamelans can be made of bronze (most usual in the case of court gamelans), iron, brass (or some combination of the two), or even bamboo.
Gamelans have grown over the centuries in both size and range. While ancient ensembles consisted almost entirely of a few bulbed gong-type instruments and had scales of two, three, or four notes, the modern court gamelan can now be played by up to thirty musicians and singers, and has over the last few hundred years incorporated some instruments which originated in other traditions, such as the double-headed skin drum, and the rebab, a two-stringed fiddle.
The Southbank Gamelan Players specialise in music from Central Java as performed in the court cities of Surakarta and Yogyakarta, with some repertoire the regions of Semarang, East Java, and from Banyumas on the border with West Java, as well as new music for gamelan.