various objects inside the piano in contact with the strings. Currently, postmodernism includes composers who react against the avant-garde and experimental styles of the late 20th century such as Astor Piazzolla, Argentina, and Miguel del Águila, USA. Minimalism In the later 20th century, composers such as La Monte Young, Arvo Pärt, Philip Glass, Terry Riley, Steve Reich, and John Adams began to explore what is now called minimalism, in which the work is stripped down to its most fundamental features; the music often features repetition and iteration. An early example is Terry Riley's In C (1964), an aleatoric work in which short phrases are chosen by the musicians from a set list and played an arbitrary number of times, while the note C is repeated in eighth notes (quavers) behind them. Steve Reich's works Piano Phase (1967, for two pianos), and Drumming (1970–71, for percussion, female voices and piccolo) employ the technique called phasing in which a phrase played by one player maintaining a constant pace is played simultaneously by another but at a slightly quicker pace. This causes the players to go "out of phase" with each other and the performance may continue until they come back in phase. According to Reich, “Drumming is the final expansion and refinement of the phasing process, as well as the first use of four new techniques: (1) the process of gradually substituting beats for rests (or rests for beats); (2) the gradual changing of timbre while rhythm and pitch remain constant; (3) the simultaneous combination of instruments of different timbre; and (4) the use of the human voice to become part of the musical ensemble by imitating the exact sound of the instruments”. Drumming was Reich’s final use of the phasing technique. Philip Glass's 1 + 1 (1968) employs the additive process in which short phrases are slowly expanded. La Monte Young's Compositions 1960 employs very long tones, exceptionally high volumes and extra-musical techniques such as "draw a straight line and follow it" or "build a fire". Michael Nyman argues that minimalism was a reaction to and made possible by both serialism and indeterminism. (See also experimental music.) Techniques Atonality and twelve-tone technique Arnold Schoenberg is one of the most significant figures in 20th-century music. While his early works were in a late Romantic style influenced by Wagner (Verklärte Nacht, 1899), this evolved into an atonal idiom in the years before the