Method of and apparatus for composing digital tone signals

摘要

Upon key depression, there is produced a phase progress signal in digital representation which varies by an increment predetermined in accordance with the frequency of the note designated by the depressed key. The phase progress signal is subjected to a coordinate conversion and squaring operation to provide downward opening parabolic curves and upwardly opening parabolic curves, which are alternately connected at their open ends to produce an approximate sinusoidal waveform as a digital tone signal. The digital tone signal is multiplied by a digital envelope signal to produce a keyed musical tone signal.