The present invention is directed to a waveform synthesizer apparatus that synthesizes a waveform of a musical sound based on musical performance event information. In particular, a music synthesizer includes an overlap detector that detects whether a first and second musical sound overlap, and a sound length meter that determines a sound length of the first musical sound. If the first and second musical sounds overlap, the synthesizer instantly terminates synthesizing of the first sound and starts synthesizing the second sound, provided the length of the first sound does not exceed a predetermined length. If the first and second sounds do not overlap, synthesis of the first sound is terminated, and the synthesis of the second sound is initiated, if it is determined that the length of rest between the two sounds does not exceed a predetermined length, and that the first sound does not exceed a predetermined length.