The tuning and construction of a gamelan orchestra is a complex process. Javanese gamelans use two tuning systems: sléndro and pélog. There are other tuning systems such as degung (exclusive to Sunda, or West Java), and madenda (also known as diatonis, similar to a European natural minor scale). In central Javanese gamelan, sléndro is a system with five notes to the diapason (octave), fairly evenly spaced, while pélog has seven notes to the octave, with uneven intervals, usually played in five note subsets of the seven-tone collection. This results in sound quite different from music played in a western tuning system. Many gamelan orchestras will include instruments in each tuning, but each individual instrument will only be able to play notes in one. The precise tuning used differs from ensemble to ensemble, and give each ensemble its own particular flavour. The intervals between notes in a scale are very close to identical for different instruments within each gamelan, but the intervals vary from one gamelan to the next.
Colin McPhee remarked, "Deviations in what is considered the same scale are so large that one might with reason state that there are as many scales as there are gamelans."[10] However, this is a view that is contested by some teachers of gamelan, and there have been efforts to combine multiple ensembles and tuning structures into one gamelan so as to ease transportation issues at the times of festivals. One such ensemble is gamelan Manikasanti, which can play the repertoire of many different ensembles.
Balinese gamelan instruments are commonly played in pairs which are tuned slightly apart to produce interference beats, ideally at a consistent speed for all pairs of notes in all registers. It is thought that this contributes to the very "busy" and "shimmering" sound of gamelan ensembles. In the religious ceremonies that contain gamelan, these interference beats are meant to give the listener a feeling of a god's presence or a stepping stone to a meditative state.
