1. A speech synthesis system comprising: a character analyzing means for analyzing a series of input characters to generate a series of syllabic symbols and a series of rhythmic symbols according to the series of input characters; a plurality of parameter file means for storing speech parameters determined by taking into consideration an influence of immediately preceding vowels of the syllabic symbols; a speech parameter generating means for generating a series of speech parameters by combining speech parameters obtained from said parameter file means in accordance with a determined vowel immediately preceding a syllabic symbol of said series of syllabic symbols; rhythmic parameter generating means for generating a series of rhythmic parameters according to the series of rhythmic symbols supplied from said character analyzing means; and a speech synthesizing means for synthesizing said series of speech parameters and said series of rhythmic parameters.