The term gamelan (also gangsa or gongsa) is used here to refer to single unified sets of instruments tuned to one of the two traditional Javanese musical scales (laras), sléndro (a five-tone scale) and pélog (a seven-tone scale). The two Javanese laras are tuning models rather than tuning standards, so each gamelan is tuned to a unique realization of one of these models. Such sets typically include dozens of instruments of various types, including ones with metal keys (metallophones), wooden keys (xylophones), and metal gongs with deep in-turned rims and a pronounced central knob. The largest of these gongs in a set is called the gong ageng (the great gong), and most gamelans in the palace have two of these impressive instruments. (See the Appendix for a listing and description of the various types of instruments found in palace gamelan sets.) A gamelan also displays a singular decorative motif on its wooden casings and racks.
A variety of types of gamelans, which can be differentiated from one another in terms of their instrumentation, tuning, repertoire, and ceremonial use, are found in the palace. A useful distinction can be made first between “archaic” gamelans and “common practice” gamelans.
Archaic gamelans, in addition to being old, include some instruments or versions of instruments that are not used in present-day gamelan practice while at the same time they lack several types of instruments that are now customary. Such gamelans were never meant to accommodate singing; some have tunings that, in comparison to modern norms, are in an atypically low register that does not complement the range of singers, while others do not even possess complete sléndro or pélog scales. Such gamelans have specific ceremonial functions and unique repertoires and performance practices associated with them. Their archaic nature is consciously preserved and effectively utilized in the palace context. Three types of archaic gamelans are found in the Yogyakarta palace: gamelan monggang, gamelan kodhok ngorèk, and gamelan sekati.
Common practice gamelans are those sets that are used for the performance of the large repertoire of central Javanese gamelan pieces (gendhings) with its associated performance practice. These ensembles can be used to accompany dance and puppet theatre and to provide music for listening pleasure. Their tuning is such that singing can be, and usually is, incorporated in their performance. Many of the older common practice gamelan sets found in the palace were constructed with instruments that have since fallen out of use (e.g., slentho and gambang gongsa; see the Appendix for descriptions). These same sets now include a number of instruments that have over time been added, some as replacements for obsolete instruments (e.g., the slenthem replaced the slentho around the turn of the 20th century), others as add-ons (e.g., gendèr panerus and the addition of many more kenong and kempul gongs than were originally constructed for a set). All but one of the common practice sets belonging to the palace that predate 1900--K.K. Pusparana--have undergone some modification to their original instrumentation.