During the 1960s, Greek composer Iannis Xenakis underwent a couple of major shifts in compositional technique. First, he implemented an algorithm that in 1962 saw the light as a complete computer program for generating musical data; this approach was entirely based on "stochastics," or probabilities. In other words, even though completely notated, his music from that period falls into the realm of indeterministic music. Soon after, though, Xenakis developed another set of tools based entirely on deterministic principles. Akrata, which was completed in 1965, falls in between, and can be seen as a transitional work. The new approach utilizes sophisticated combinatorial techniques, combining various sets of musical elements into ordered sequences. This style is evident in Akrata right from the start: single repeated notes are passed around the brass instruments, all scored in the mid-range octaves. There are no recognizable rhythms, and the effect is rather like a kaleidoscope, with the timbre, or tonal color, being the main element by which the musical architecture is delineated.
Akrata is a Greek term for "pure," and certainly this is unadorned music. There are no melodies to speak of, no catchy rhythmic patterns, no harmonic progressions in the usual sense. Instead, the piece proceeds on the basis of shifting densities, dynamics, and instrumental sonorities. If it is "about" anything, Akrata is a study in building a musical structure based on ever-changing, but extremely limited, combinations of elements. The energy is created by the sharp articulations of the repeated notes as they are passed around the ensemble. The musical flow is faltering, though, as the sounds keep breaking off into silence.
Akrata also showcases Xenakis' use of "non-sound" as a structural component -- the treatment of silence as an equal to sound rather than just as an articulator of structural units (i.e., marking the ends of phrases or sections). It has a strange, austere beauty that is exemplary of the minimalist element that gained artistic prominence in the 1960s.