Terry Riley -- inventor of the repetitive, patterned musical style known as Minimalism -- has been a serious student of North Indian classical music since 1970, and his original music has borne its influence. His pieces, with instrumentation ranging from acoustic to electronic, often start with repeating riffs or drones which he overlays with intricately woven melodic lines and patterns derived from ragas, North Indian folk melodies. Though the patterns move quickly, the underlying harmonies remain the same throughout each piece. This harmonic stasis, which brings the listener into a peaceful, dreamlike trance, profoundly influenced the new age and ambient musical movements of the 1980s and '90s. Some of Riley's work involves more propulsive rhythms and veers closer to progressive rock, while his acoustic music for piano and saxophones recalls the world fusion experiments of jazz artists in the early 1970s.