  This paper presents the Computoser hybrid probability/rule based algorithm
for music composition (http://computoser.com) and provides a reference
implementation. It addresses the issues of unpleasantness and lack of variation
exhibited by many existing approaches by combining the two methods (basing the
parameters of the rules on data obtained from preliminary analysis).
  A sample of 500+ musical pieces was analyzed to derive probabilities for
musical characteristics and events (e.g. scale, tempo, intervals). The
algorithm was constructed to produce musical pieces using the derived
probabilities combined with a large set of composition rules, which were
obtained and structured after studying established composition practices.
Generated pieces were published on the Computoser website where evaluation was
performed by listeners. The feedback was positive (58.4% approval), asserting
the merits of the undertaken approach.
  The paper compares this hybrid approach to other approaches to algorithmic
composition and presents a survey of the pleasantness of the resulting music.
