One of the most important 20th-century composers, Igor Stravinsky (1882–1971), wrote music with very complicated (difficult) chords (groups of notes that are played together) and rhythms. Some composers thought music was getting too complicated and so they wrote Minimalist pieces which use very simple ideas. In the 1950s and 1960s, composers such as Karlheinz Stockhausen experimented with electronic music, using electronic circuits, amplifiers and loudspeakers. In the 1970s, composers began using electronic synthesizers and musical instruments from rock and roll music, such as the electric guitar. They used these new instruments to make new sounds.