A computer music performance system (CMPS) is a computer system connected to input devices (including musical keyboards or other instruments) and to graphic and audio output devices. A human performer generates input events using the input devices. The CMPS responds to these events by computing and performing sequences of output actions whose intended timing is determined algorithmically. Because of the need for accurate timing of output actions, the scheduling requirements of a CMPS differ from those of general-purpose or conventional real-time systems.

This paper describes the scheduling facilities of FORMULA, a CMPS used by many musicians. In addition to providing accurate timing of output action sequences, FORMULA provides other basic functions useful in musical applications: 1) per-process virtual time systems with independent relationships to real time; 2) process grouping mechanisms and language-level control structures with time-related semantics, and 3) integrated scheduling of tasks (such as compiling and editing) whose real-time constraints are less stringent than those of output action computations.




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