Georgia has an ancient musical tradition, which is primarily known for its early development of polyphony. Georgian polyphony is based on three vocal parts, a unique tuning system based on perfect fifths, and a harmonic structure rich in parallel fifths and dissonances. Three types of polyphony have developed in Georgia: a complex version in Svaneti, a dialogue over a bass background in the Kakheti region, and a three-part partially-improvised version in western Georgia. The Georgian folk song "Chakrulo" was one of 27 musical compositions included on the Voyager Golden Records that were sent into space on Voyager 2 on 20 August 1977.