How to Compose Aleatoric Music. Aleatoric music, sometimes referred to as chance music, is music in which some element of the composition and/or performance is left up to chance. Often, this results in performances that differ every time depending on the player. Because of this factor, aleatory music is sometimes also called indeterminate music. The avant-garde composer John Cage was a great proponent of aleatoric music. Karlheinz Stockhausen was another composer of aleatoric music.
Begin composing a piece of aleatoric music by creating a theme. This theme will become the central motif of the song.
Expand on the core theme by composing a variation in a different key or tempo. This will be used to build the overall composition. Once the composition has been created in the normal fashion, aleatoric elements can be added.
Offer a variety of options for performers throughout the piece. These can be a choice of changes in key, tempo or time signature. These should be indicated on the sheet music as a series of options such as A, B, C and D. The individual performers are then allowed to select one of the options at their discretion. Each of these options must be musically valid.
Allow singers to repeat words at random during certain segments of the song. This aleatoric technique was used by Eric Whitacre's in his composition "Cloudburst."
Use a sequencer to create randomized sequences during a song. The sequencer's random number generation software will create an endless variation.