Pithoprakta (1956) is a piece by Iannis Xenakis for 46 string instruments, two trombones, xylophone, and woodblock. Premiered by conductor Hermann Scherchen in Munich on March 1957, the piece was made into a ballet by George Balanchine, Metastaseis and Pithoprakta, along with the earlier Metastaseis.
The title translates as "actions through probability", and the piece is based on the statistical mechanics of gases, Gauss's law, or Brownian motion. Each instrument is conceived as a molecule obeying the Maxwell–Boltzmann distribution law, with Gaussian distribution of temperature fluctuation.
Brownian motion is a four-dimensional phenomenon (three-dimensions and time), and Xenakis created the score by first creating a two-dimensional graph, necessitating some simplifications. The abscissa (x) represents time at 5 cm = 26 MM, while the ordinates (y) represent pitch at 1 semitone = .25 cm. When transcribed into musical notation 5 cm = one measure. This length is subdivided into three, four, and five equal parts, allowing for fine differences in duration, but also creating a steady pulse in each instrument part, reducing the rhythm of the random walk to steady footsteps ("a situation impossible in [the] reality [of the model]"). Each part gets nowhere, but as a whole the mass's pitch is freely modulated and its speed determined "temperature" varies.
- Harley, James (2004). Xenakis: His Life in Music, p.13. Routledge. ISBN 0-415-97145-4.
- Ilias Chrissochoidis, Stavros Houliaras, and Christos Mitsakis, "Set theory in Xenakis' EONTA", in International Symposium Iannis Xenakis, ed. Anastasia Georgaki and Makis Solomos (Athens: The National and Kapodistrian University, 2005), 241–249.
- Xenakis, Iannis (1992). Formalized Music: Thought and Mathematics in Composition, p.15. ISBN 9781576470794.
- Emmerson, Simon (2007). Living Electronic Music, p.48. ISBN 9780754655480.
- Randel, Don Michael (1996). The Harvard Biographical Dictionary of Music, p.999. ISBN 9780674372993.
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