Software sound source

A music apparatus uses a processing unit of a universal type having an extended instruction set used to carry out parallel computation steps in response to a single instruction which is successively issued when executing a program. A software module defines a plurality of channels and is composed of a synthesis program executed by the processing unit using the extended instruction set so as to carry out synthesis of waveforms of musical tones through the plurality of the channels. The plurality of the channels are optimally grouped into parallel sets each containing at least two channels. The synthesis of the waveforms of at least two channels belonging to each parallel set are carried out concurrently by the parallel computation steps. A buffer has a capacity sufficient to store the waveform samples allotted to one frame period. A cache has a capacity sufficient to store a subset of the waveform samples which is an integer division of the set allotted to one frame period. The synthesis program is executed by the processing unit at one frame period so as to carry out synthesis of a set of waveform samples allotted to one frame period while efficiently accessing the cache. Any designated subroutine programs are sequentially called in response to call instructions to process the waveform samples during the synthesis.