Process Music - Theory

Theory

Michael Nyman has identified five types of processes (Nyman 1974, 5–8):

1. Chance determination processes, in which the material is not determined by the composer directly, but through a system he or she creates
2. People processes, in which performers are allowed to move through given or suggested material, each at his or her own speed
3. Contextual processes, in which actions depend on unpredictable conditions and on variables arising from the musical continuity
4. Repetition processes, in which movement is generated solely by extended repetition
5. Electronic processes, in which some or all aspects of the music are determined by the use of electronics. These processes take many forms.

The first type is not necessarily confined to what are normally recognised as "chance" compositions, however. For example, in Karel Goeyvaerts’s Sonata for Two Pianos, "registral process created a form that depended neither on conventional models nor … on the composer’s taste and judgment. Given a few simple rules, the music did not need to be 'composed' at all: the notes would be at play of themselves” (Griffiths 2011, 38).

Galen H. Brown acknowledges Nyman's five categories and proposes adding a sixth: mathematical process, which includes the manipulation of materials by means of permutation, addition, subtraction, multiplication, changes of rate, and so on (Brown 2010, 186).

Erik Christensen identifies six process categories (Christensen 2004, 97):

1. Rule-determined transformation processes
2. goal-directed transformation processes
3. indeterminate transformation processes
4. Rule-determined generative processes
5. goal-directed, and generative processes
6. indeterminate generative processes

He describes Reich's Piano Phase (1966) as rule-determined transformation process, Cage's Variations II (1961) as an indeterminate generative process, Ligeti's In zart fliessender Bewegung (1976) as a goal-directed transformation process containing a number of evolution processes (Christensen 2004, 116), and Per Nørgård's Second Symphony (1970) as containing a rule-determined generative process of a fractal nature (Christensen 2004, 107).