Central Javanese gamelan
A modern Central Javanese gamelan, such as the one pictured above, consists mainly of tuned metallophones and gongs and gong chimes with other instruments (see below).
A complete gamelan is actually two sets of instruments, in different laras (tunings), namely slendro (a five-tone scale) and pelog (a seven-tone scale). However the precise tuning of each individual gamelan is unique.
The 'traditional' Javanese music usually played today originates largely from the 19th century Javanese courts, although some of this music has much older origins.
The pieces are cyclical in nature, with some instruments playing a basic melody, others embellishing this while others act as 'punctuation' to mark important points in each cycle.
Gongs, Suwukan and Kempul
These are shown at the back of the main picture above. The big gong is the most important instrument in the ensemble and is used to mark the end of each cycle.
Kenong (left) are also 'punctuating' instruments.
The saron (middle right of the main picture above) play the basic melody (balungan) of the piece.
The demung plays an octave below the saron and the peking plays an octave above.
The balungan is also played by the slenthem, a metallophone with bamboo resonators.
These are horizontal gong-chimes (at the front left of the main picture above) which play straightforward embellishments on the main melody.
Double-headed drums which lead the ensemble.
gender - metallophones with bamboo resonators
gambang - wooden xylophone-like instruments
rebab - a two-stringed bowed instrument
suling - an end-blown bamboo flute
siter - a zither-like instrument.
All these instruments play embellishments on the basic melody.
Resource Link http://www.gamelannetwork.co.uk/javanese-gamelan.html