David P. Anderson
Abstract
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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Index Terms
- A system for computer music performance
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Reviews
Rosa Michaelson
Some composers and performers wish to use computers to generate and control sound. To this end, various systems, here called computer music performance systems (CMPSs), have been designed. The authors have developed software that will allow a Motorola 68000 machine that runs Forthmacs to control certain “musical events” prescribed by the user. Though it is difficult to imagine the music produced by a CMPS, the music events might be MIDI signals to a synthesizer, graphical displays, or sounds generated from the clock. The authors give a general definition of a CMPS and then describe their own CMPS, which has an associated language (or Forthmacs library) called FORMULA. FORMULA programming features and implementation are discussed. This paper is concerned with some of the scheduling problems associated with real-time generation of these musical events. The problems of timing certain musical activities and the algorithms for solving such problems are covered at some length. The paper is technical and is aimed at computer scientists rather than musicians. A useful discussion of existing work in the field gives pointers for associated reading. I found this paper thoughtful and well presented. An appendix with a full description of the FORMULA language would have helped the reader understand the scheduling solutions, which are shown by top-level routine calls. While the scope of this paper does not require evaluation from performers or composers, I wonder how many can program in FORMULA or are computer-literate enough to follow this paper. Despite these caveats, the problems of scheduling musical events in CMPS constitute an interesting research topic. I look forward to more work from these authors, perhaps on the human interface design.
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