PURPOSE: To simulate human speech by speech synthesis by determining and storing parameters necessary to control speech synthesis, forming the weighted mean value of the curves defined by the control parameters, and joining polyphones.

CONSTITUTION: Parameters necessary to control speech synthesis are determined, the control parameters are stored in one matrix or one sequence list for each polyphone, and the behavior around each phoneme boundary is defined with time for two control parameters. The duration time of the phoneme in each polyphone is matched to the adjacent polyphone determined by quantization of the sampling time interval for one parameter, and the weighted mean value of the curve defined by the stored control parameters is formed so as to join polyphones. Thus, speech is synthesized by using formant synthesis, and natural speech is duplicated by two-sound synthesis to simulate human speech.