rather than as required. Common Music is implemented in Common Lisp and CLOS

Guy Steele, Common Lisp: The language, Digital Press 1990

and is source compatible across a whole host of computer platforms without modifying any of the source code. This provides obvious leverage for a composer since, by virtue of being portable, the system may be used in conjunction with programs, languages and devices that are not. For example, using Common Music on the NeXT computer allows a composer to take advantage of the Music Kit,

David Jaffe, Musical and Extra-Musical Applications of the NeXT MusicKit,

 in: Proceedings of the 1991 International Computer Music

Conference, Montreal 1991, pp. 521-524

a real-time synthesis language that runs only in the NeXTStep operating environment.

System Architecture

Common Music may be viewed, in part, as a music language for controlling other music languages and programs. This control strategy involves three general levels of abstraction. The highest level might be termed the compositional level in which musical structure and pattern is explored and defined. The middle level is the synthesis level, in which specific sound descriptions (generally described as sets of sound parameter values) are transformed by some synthesis technique to a very low level representation of sound. The lowest level is the performance level in which the output from a synthesis program is made audible (and perhaps visible) by some physical device such as a DAC or a synthesizer or windowing system (Figure 1).

In terms of this organization, Common Music represents the highest compositional level. Its basic function is to automatically transform high level representations of compositional structure and patterns into a representation that is understandable by the various syntheses languages represented by the second level. As mentioned in the preceding section, this transformation is accomplished 'invisibly' through a notion of output syntax. An output syntax is a named collection of methods and event stream classes that implement input and output processing for various external music systems or protocols supported by the system: MIDI, Common Lisp Music (CLM),

William Schottstaedt, Common Lisp Music, Unpublished Software

Document 1992, CCRMA Stanford University

Music Kit, CSound and CMN,

William Schottstaedt, CMN Computing in Musicology 8, 1992

a music notation package.

Both real time and file based processing are supported through a generic input/output protocol specialized to various classes of musical objects and event streams. By selecting a new syntax the identical compositional material is able to produce completely different results.