lated by simple circuits that are easy to design when vibrato sounds are required. First, the analysis of performed musical sounds in order to define the location of principal pitch of vibrato sounds was attempted. But, a definite answer has not been obtained from this approach. As Shonle and Horan2) state, the results of various experiments have variously indicated that principal pitch is localized in the higher side of the extent of vibrato,3) another in the middle,4) and yet another in the lower side.5) This discrepancy results from the fact that musical sounds are not played similar to notes because of the Abraham effect6) or artistic deviation.7) Consequently, it is difficult to locate the principal pitch of vibrato sounds through this approach.