Experimental music

The score for John Cage’s indeterminate composition “Fontana Mix”

“Experimental music is a general label for any music that pushes existing boundaries and genre definitions. Experimental compositional practice is defined broadly by exploratory sensibilities radically opposed to, and questioning of, institutionalized compositional, performing, and aesthetic conventions in music. 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. Artists may also approach a hybrid of disparate styles or incorporate unorthodox and unique elements. The practice became prominent in the mid-20th century, particularly in Europe and North America. John Cage was one of the earliest composers to use the term and one of experimental music’s primary innovators, utilizing indeterminacy techniques and seeking unknown outcomes. 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. 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. … 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, Steve Reich, etc.), as well as composers such as Gavin Bryars, John Cale, Toshi Ichiyanagi, Cornelius Cardew, John Tilbury, Frederic Rzewski, and Keith Rowe.  …”
Wikipedia
Smithsonian: 5 1/2 Examples of Experimental Music Notation (Video)
Rock, Pop, and the Development of Avant Garde Music After World War II
Deutsche Courage: The Boundary-Breaking Minds Behind Experimental German Music (Video)
YouTube: The Rise of Experimental Music in the 1960s documentary 49:57, Early Electronic Experimental Ambient Avant garde Abstract Noise Minimal Musique concrete 59:54, etc.

Henry Cow in Cambridge