"When John Cage and many other
composers started to seek
for the chance, indeterminacy or improvisation in the late 1950s,
Xenakis proposed the stochastic music.
It is a mathematical method to construct
unknown, but overall controlled complex sound movements
from the repeated random trials.
Without any musical premises
such as theme, tone row or rhythmic patterns,
using only Poisson distributions and other probability functions,
one can determine every phase
from the pitch, duration,
density (number of sound within a unit time), timbre distribution
to the overall structure (macro composition).
With this method Xenakis composed a series of instrumental music
starting with "Achorripsis"(1958) for 21 instruments
and then "ST10", etc. with a computer program."
