This post discusses the procedural and aleatory (or stochastic) nature of the sound pieces which appear on pioneering post-WWII composer Iannis Xenakis’s “Electro-Acoustic Music” LP.
Something is procedural in that it’s based on a given instruction — it’s algorithmic, but not necessarily computer-produced. Visual artist Sol Lewitt popularized the procedural generation of art throughout the development of mid-twentieth century minimalism, while composer John Cage is best known for pioneering similar techniques in music composition — both artists involving the use of aleatoric properties, or “the incorporation of chance into the process of creation.” (src)
Xenakis utilized both aleatoric and procedural methods in the creation of compositions like Concret P–H (which was a site-specific composition for the presentation of Le Corbusier’s Pavilion), Bohor, Diamorphoses, and Orient-Occident (all of which were later released together by Nonesuch in 1970). These tracks were composed through cutting-edge (at the time) techniques from splicing tape loops to computational methods to create non-representational sounds, a process and set of characteristics known as musique concrète.
Aleatoricism appears in how Xenakis used computational methods to apply mathematical models to compose his music, particularly stochastic processes: “a random process evolving with time” (src), which is to say that “some element or variable is governed by chance” (src). Where a traditional composition would be completely deterministic, Xenakis’s works introduced a probabilistic element. These methods are also procedural: “[Xenakis] composes a general structure, with broadly defined formal shape, density, etc, and then uses statistics (usually with the aid of a computer) to generate the details (i.e. the specific pitches and rhythms) that will create that structure.”(src) What’s interesting about this is the question of whether stochastic methods could truly be considered aleatoric if the probabilistic element is itself set within a deterministic structure, insofar that it’s statistically predictable. In a discussion regarding the semantic differences, a Wikipedia editor points out that “Stochastic music does involve chance, but to a comparatively limited degree and on a very local level. It also results in more traditional, determinate scores, without room for performer choice… all stochastic music is aleatory to some degree, but not all aleatory music is stochastic.” (src)
Although Xenakis’s stochastic approach may indeed be aleatoric, it is interesting how the work’s procedural methods put its aleatoric nature to question — what is chance anyway? Randomness can only be observed when there isn’t enough statistical data to reveal the pattern. Randomness may be more easily observed in the physical world where there are innumerable variables at play. In Electro-Acoustic Music, Xenakis confronts this notion: “Splicing of innumerable little pieces of tape (the sound source is the discharge of smouldering charcoal) and mixing to obtain varying densities were the two main techniques employed in Concret P-H… Despite the fact that Xenakis uses many computational methods, both manual and mechanized, to construct his instrumental works, his electro-acoustic music is not the direct result of mathematical operations. The sounds that are used possess by their nature the qualities of which the mathematical formulae are abstracted reflections. Thus, instead of working “outside of time” to find general mathematical structures which then give rise to specific temporal events, Xenakis feels that there is a direct contact with materials that have statistical properties,” like the smoldering charcoal, “and he approaches the work in the manner of sculpture.” (James Mansback Brody via “Electro-Acoustic Music”, cover text; emphasis my own)