Experimental music is a compositional tradition that arose in the mid-20th century, particularly in North America, of music composed in such a way that its outcome is unforeseeable. The American composer John Cage is seen as one of the more notable composers associated with this music. In France, as early as 1953, Pierre Schaeffer had begun using the term "musique expérimentale" to describe compositional activities that incorporated tape music, musique concrète, and elektronische Musik. Also, in America, a quite distinct sense of the term was used in the late 1950s to describe computer-controlled composition associated with composers such as Lejaren Hiller. In 1958, Hiller became the first director of the Studio for Experimental Music at University of Illinois at Urbana-Champaign.
The Groupe de Recherches de Musique Concrète (GRMC), under the leadership of Pierre Schaeffer, organized the First International Decade of Experimental Music between 8 and 18 June 1953. John Cage was also using the term as early as 1955. Composer and critic Michael Nyman starts from Cage's definition and develops the term "experimental" also to describe the work of other American composers (Christian Wolff, Earle Brown, Meredith Monk, Malcolm Goldstein, Morton Feldman, Terry Riley, La Monte Young, Philip Glass, John Cale, Steve Reich, etc.), as well as composers such as Gavin Bryars, Toshi Ichiyanagi, Cornelius Cardew, John Tilbury, Frederic Rzewski, and Keith Rowe.
Harry Partch as well as Ivor Darreg worked with other tuning scales based on the physical laws for harmonic music. For this music they both developed a group of experimental musical instruments. Musique concrète (French; literally, "concrete music"), is a form of electroacoustic music that utilises acousmatic sound as a compositional resource. Free improvisation or free music is improvised music without any rules beyond the taste or inclination of the musician(s) involved; in many cases the musicians make an active effort to avoid overt references to recognizable musical genres.
Elements of experimental music include indeterminate music, in which the composer introduces the elements of chance or unpredictability with regard to either the composition or its performance. There are many ideas broadly utilized by experimental musicians which are not, however, strictly experimental music concepts, having seen significant application prior to the advent of experimental music, particularly by the avant garde. Examples include: extended techniques (Instrumental or vocal performance techniques that step outside (often far outside) conventional performance techniques) and graphic notation (music which is written in the form of diagrams or drawings. Other elements include "Prepared" instruments—ordinary instruments modified in their tuning or sound-producing characteristics; using instruments, tunings, rhythms or scales from non-Western musical traditions; using sound sources other than conventional musical instruments, such as trash cans, telephone ringers, or doors slamming; creating experimental musical instruments for enhancing the timbre of compositions and exploring new techniques or possibilities; using a tape loop to create a tape phase; and removing perceived barriers of traditional concert settings by putting performers scattered among the audience.