PLA is a software designed to help the composer in writing computer scores, able to speed up the work of defining the musical parameters; generating outputs also compatible with many other software or computer music systems.
Brief History – Pla has been developed in 1983 by Bill Schottstaedt at CCRMA (Center for Computer Research in Music and Acoustics), Stanford University. This is a program that was designed to facilitate the music composition through the computer, for this was accomplished by allowing its use in conjunction with other software or systems for computer music, such as Music V, Mus10, MusBox or Samson Box.
Antecedents – Among the programs of its kind, Pla did not present itself as something new: in previous years, in fact, were created software as Scot or the most famous Score, by Leland Smith. These were computer tools that allowed to quickly write the score file: a code section that, in a music compiler like Music V, was used to specify parametres such as sounds frequency, duration, amplitude envelopes, sounds to be played and many other information for music performance.
Features – In this sense, then, Pla did not differ much from the past. Developed with SAIL programming language, Pla was organized to bring as much as possible the needs of composers, avoiding them to learn in detail the operation of computers.
Graphical Output – Among the features of Pla, some of which were also made by Michael McNabb, the most interesting, that most distinguishes this software from his earlier, is related to the ability to obtain graphical representations of musical parameters, such as reporting on the Cartesian axes frequencies and durations of sound signals.
Limits – Beyond these innovative features, and the fact that it was developed with the intention of bringing the needs of composers, PLA has been a project that was not carried forward over the years. What acted more on its disappearance was probably the limited portability that, as specified by Schottstaedt, it was not an aspect taken into consideration between work goals. Nevertheless, Pla has played an important role in the development of other software, especially by inspiring the creation of Common Music by Heinrich Taube.
PLA’s use – Schottstaedt’s software, beyond all, has been used in various compositions. We remember in particular some works by David Jaffe: All Your Children May Be Acrobats (1981) and, more importantly, Silicon Valley Breakdown. The latter is contained in the collection Dinosaur Music which includes some musical works made with the Samson Box and Pla.
For this topic I’ve read:
 Bill Schottstaedt, PLA: A Composer’s Idea of a Language, in The Music Machine, edited by Curtis Roads, The MIT Press, 1989.