Gamelan is the traditional ensemble music of Java and Bali, primarily made up of percussion instruments. The ensemble includes bronze metallophones, gongs, xylophones, and drums. A unique aspect of the Gamelan is that the instruments are built and tuned as a set; you cannot swap a gong from one ensemble to another because each Gamelan has its own unique tuning. The music is characterized by 'interlocking patterns' called kotekan, where two or more players alternate notes to create a rapid, complex melody that would be impossible for one person to play. In Bali, Gamelan is often used in 'Kebyar' style, which is explosive and dynamic. The sound is often described as 'shimmering' because the instruments are tuned in pairs to slightly different frequencies, creating an acoustic 'beat' or vibrato.