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Aleatoric music, also known as aleatory music, is music with a random element. Chance elements within a piece can be used for composition, as well as for live performance. When a piece is being composed, random elements can be used to influence the outcome of a final musical piece. In a live performance, chance can be used to determine how a piece is played. Aleatoric music differs from improvisational music because improvisational music is composed on the spot by a musician, while true aleatoric music has elements that are decided through random chance.
This type of music is mostly designed by a composer who has decided to allow chance to decide some elements of the music. This can include randomizing musical sequences or using chance to determine the notes played in a musical piece. A composer can also use randomness to select other elements of the music, including its tempo, its key and the instruments playing in the piece. Composers who use this technique often flip a coin or roll dice to determine how the musical piece will progress. Well-known composers of aleatoric music include Karlheinz Stockhausen, Witold Lutoslawski, and John Cage.
Random elements in this music are chosen using methods like flipping a coin, rolling a pair of dice, or by using a random numbers generator. Generally, chance is allowed to define either the form or the content of a musical piece, but it can also be used to define elements of both. The idea of this type of music is that some of the elements are controlled by the composer, and some are chosen by the roll of the dice. In aleatoric music, in addition to deciding the non-random elements of the piece, the composer also decides how much chance should influence the musical work.
In live music, aleatoric music usually comes in the form of a written piece that differs in performance due to some random element of variation. Generally, special musical pieces are written for the purpose of having their parts played at random. A chance element can be used to determine the order in which song sections are played, the instruments playing in the piece and many other elements of a musical performance.
If the conductor of a music group rolls the dice before a performance to determine key elements of the music, this is aleatoric music. The random element that is used to apply chance to the piece is called the aleatory variable. Using randomness in the process of creation is called aleatoricism. This method of creating art has also been used as an experimental method of presenting films, generally by independent filmmakers.