Aleatoric musicwikipedia
Aleatoric music (also aleatory music or chance music; from the Latin word alea, meaning "dice") is music in which some element of the composition is left to chance, and/or some primary element of a composed work's realization is left to the determination of its performer(s).
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Music

musicaudiomusical
Aleatoric music (also aleatory music or chance music; from the Latin word alea, meaning "dice") is music in which some element of the composition is left to chance, and/or some primary element of a composed work's realization is left to the determination of its performer(s).
Music that makes heavy use of randomness and chance is called aleatoric music, and is associated with contemporary composers active in the 20th century, such as John Cage, Morton Feldman, and Witold Lutosławski.

John Cage

John CageCageCage, John
American composer John Cage's Music of Changes (1951) was "the first composition to be largely determined by random procedures", though his indeterminacy is of a different order from Meyer-Eppler's concept.
Through his studies of Indian philosophy and Zen Buddhism in the late 1940s, Cage came to the idea of aleatoric or chance-controlled music, which he started composing in 1951.

Charles Ives

IvesCharles IvesIves, Charles
The earliest significant use of aleatory features is found in many of the compositions of American Charles Ives in the early 20th century.
He combined the American popular and church-music traditions of his youth with European art music, and was among the first composers to engage in a systematic program of experimental music, with musical techniques including polytonality, polyrhythm, tone clusters, aleatory elements, and quarter tones, foreshadowing many musical innovations of the 20th century.

Karlheinz Stockhausen

StockhausenKarlheinz StockhausenStockhausen, Karlheinz
Other early European examples of aleatory music include Klavierstück XI (1956) by Karlheinz Stockhausen, which features 19 elements to be performed in a sequence to be determined in each case by the performer.
He is known for his groundbreaking work in electronic music, for introducing controlled chance (aleatory techniques or aleatoric musical techniques) into serial composition, and for musical spatialization.

Pierre Boulez

BoulezPierre BoulezBoulez, Pierre
In Europe, following the introduction of the expression "aleatory music" by Meyer-Eppler, the French composer Pierre Boulez was largely responsible for popularizing the term.
As a young composer in the 1950s he quickly became a leading figure in avant-garde music, playing an important role in the development of integral serialism and controlled chance music.

Witold Lutosławski

LutosławskiWitold LutosławskiLutoslawski, Witold
Some scholars regard the resultant blur as "hardly aleatory, since exact pitches are carefully controlled and any two performances will be substantially the same" although, according to another writer, this technique is essentially the same as that later used by Witold Lutosławski.
It also uses aleatoric processes, in which the rhythmic coordination of parts is subject to an element of chance.

Graphic notation (music)

graphic notationgraphic scoresgraphic score
From this point of view, indeterminate or chance music can be divided into three groups: (1) the use of random procedures to produce a determinate, fixed score, (2) mobile form, and (3) indeterminate notation, including graphic notation and texts.
Other uses include pieces where an aleatoric or undetermined effect is desired.

Indeterminacy (music)

indeterminacyindeterminateindeterminate music
American composer John Cage's Music of Changes (1951) was "the first composition to be largely determined by random procedures", though his indeterminacy is of a different order from Meyer-Eppler's concept.
In Europe, following the introduction of the expression "aleatory music" by Meyer-Eppler, the French composer Pierre Boulez was largely responsible for popularizing the term.

Alan Hovhaness

Alan HovhanessHovhaness, AlanHovhaness
Later American composers, such as Alan Hovhaness (beginning with his Lousadzak of 1944) used procedures superficially similar to Cowell's, in which different short patterns with specified pitches and rhythm are assigned to several parts, with instructions that they be performed repeatedly at their own speed without coordination with the rest of the ensemble.
Lousadzak was Hovhaness's first work to make use of an innovative technique he called "spirit murmur", an early example of aleatoric music inspired by a vision of Hermon di Giovanno. The technique, essentially similar to the 1960s ad libitum aleatory of Lutoslawski, involves instruments repeating phrases in uncoordinated fashion, producing a complex "cloud" or "carpet" of sounds..

Marcel Duchamp

Marcel DuchampDuchampDuchampian
The French artist Marcel Duchamp composed two pieces between 1913 and 1915 based on chance operations.
The two compositions are based on chance operations.

Henry Cowell

Henry CowellCowell, HenryCowell
Henry Cowell adopted Ives’s ideas during the 1930s, in such works as the Mosaic Quartet (String Quartet No. 3, 1934), which allows the players to arrange the fragments of music in a number of different possible sequences.
In the early 1930s, Cowell began to delve seriously into aleatoric procedures, creating opportunities for performers to determine primary elements of a score's realization.

Klavierstücke (Stockhausen)

KlavierstückeKlaviKlavierstück XIKlavierstück XI
Other early European examples of aleatory music include Klavierstück XI (1956) by Karlheinz Stockhausen, which features 19 elements to be performed in a sequence to be determined in each case by the performer.
Klavierstück XI is famous for its mobile, or polyvalent structure.

Aleatoricism

aleatoricaleatoryaleatoricism
The term aleatory music was first coined by Werner Meyer-Eppler in 1955 to describe a course of sound events that is "determined in general but depends on chance in detail".

Lousadzak

Piano Concerto (''Lousadzak'')
Later American composers, such as Alan Hovhaness (beginning with his Lousadzak of 1944) used procedures superficially similar to Cowell's, in which different short patterns with specified pitches and rhythm are assigned to several parts, with instructions that they be performed repeatedly at their own speed without coordination with the rest of the ensemble.
The work is known for its use of aleatory.

Music of The Lord of the Rings film series

Lord of the RingsThe Lord of the RingsThe Lord of the Rings: The Two Towers
The score uses a neo-romantic, 19-century style and structure, derived from Shore's desire to have the music sounding antiquated, but he nevertheless married it to modern and at times avant-garde techniques including atonal sections, unusual instrumental choices and orchestral set-ups, aleatoric writing, sprechstimme voices and syncopated rhythms, as well as borrowing from eastern scales, medieval styles of music, contemporary film music idioms for specific setpieces, classical idioms for some of the music of the Shire, new-age and contemporary idioms for the end-credits songs, etc. However, he insisted on staying away from electronic or synthesized music.

Source: Music of the Avant Garde

Source
The 11 issues document new music practices of the period like indeterminacy, performance, graphic scores, electronic music and intermedia arts.

Experimental pop

experimental popexperimental pop musicexperimental
It may incorporate experimental techniques such as musique concrète, aleatoric music, or eclecticism into pop contexts.

Burr Van Nostrand

Burr Van Nostrand
He is known for his avant-garde works which use aleatory and graphic notation and were composed from the 1960s through the 1980s.

Symphony No. 1 (Schnittke)

Symphony No. 1First Symphony
Scored for a very large orchestra, it is recognised as one of Schnittke's most extreme essays in aleatoric music: from the outset the piece is loud, brash and chaotic, and it imports motifs from all parts of the Western classical tradition.

Plus-Minus (Stockhausen)

Plus-MinusPlus MinusPlus-Minus'' (Stockhausen)
Plus-Minus is a "polyvalent process composition", designed as a project for the composition students attending the first Cologne Courses for New Music, held at the Rheinische Musikhochschule in October to December 1963.

Rodion Shchedrin

Rodion ShchedrinShchedrinShchedrin, Rodion
Shchedrin's early music is tonal, colourfully orchestrated and often includes snatches of folk music, while some later pieces use aleatoric and serial techniques.

Wind chime

wind chimewindchimeschimes
Since the percussion instruments are struck according to the random effects of the wind blowing the chimes, wind chimes have been considered an example of chance-based music.