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.