In Hip hop music, people individually and separately vocalize over beats, instrumental tracks, usually consisting of repeated phrases. Hip-hop is considered an important development in the history of music because, for the first time, non-tonal aspects of speech, its emphasis and lyricism, are the most identifiable aspects of vocalizations. Also, syncopation and abstract rhythms are being used in ways never before. In addition, technological manipulation of sound is being used as never before. Hip-hop began as an idea during the 1970s, became a mainstream genre during the 1980s, and an internationally popular genre during the 1990s and 2000s. It is usually divided into three periods: Roots, Old School, and Golden Age. Most agree that the "golden age" ended during the 1990s. The current period is not yet named, though it is commonly referred to as New school hip hop.