Quartet for Guitars by Herbert Bielawa
(Dr. Herb Bielawa is the founder and director of the electronic music studio at San Francisco State University).
Quartet for Guitars was written in conjunction with a paper, Macrostructure in Composition. The piece was performed at 1750 Arch St. April 11 by the San Francisco Guitar Quartet, and at concerts by Bielawa's performance group Pro Musica Nova at Stanford April 15 and S.F. State April 29, by a quartet including Rani Cochran, who edited the piece.
From the program notes: "The piece's basic structure, called a 'density envelope,' was literally drawn out, graph-style, over the entire range of the guitar to determine a bank of all possible pitches available at a given moment in the piece. This envelope was then fed into a computer to determine a random selection of notes to be played from the pitch bank. The durations of notes were determined using a statistical plan based on the unit of the sixteenth note. This plan was then in turn fed into a computer to determine the order in which the durations appear."