A sample counter in each channel performs counting operation at a given rate. Independently for each channel, the rate and an initial value for the counter are set, and start and stop of the counting operation of the counter are controlled, so that a partial portion of an original waveform corresponding to a count range from the set initial value to a count stop point is reproduced in the channel. A control section sets the initial values in individual ones of a set of channels, selected from among the channels, such that sample values at different sample positions of the original waveform are simultaneously retrieved in individual ones of the set of channels, and controls an overlap adder to add up the retrieved sample values, so that sample values of an audio waveform signal with a plurality of partial portions of the original waveform, partially overlapping each other are output.