A plurality of blocks of waveform data are stored in a memory, which also stores, for each of the blocks, synchronizing information representative of a plurality of cycle synchronizing points that are indicative of periodic specific phase positions where the block of waveform data should be synchronized in phase with another block of waveform data. Two blocks of waveform data (e.g., harmonic and nonharmonic components) are read out from the memory, along with the synchronizing information. On the basis of the synchronizing information, the readout of two blocks of waveform data is controlled using the synchronizing information. There is stored, for each of the blocks, at least one piece of synchronizing position information indicative of a specific position where the block should be synchronized with another block, and the readout of the individual blocks of waveform data is controlled so that the blocks are synchronized with each other using the synchronizing position information.