21. A method for recognizing a string of spoken characters comprising the steps of: storing a plurality of reference character sets in predetermined groups; generating a set of signals representative of the acoustic features of spoken reference characters; generating a signal representative of the acoustic features of each spoken input characters; producing a set of signals representative of the acoustic correspondence of the input characters to said reference characters jointly responsive to the input character acoustic feature signals and the reference character acoustic feature signals; and identifying the input character string as one of the stored reference character sets responsive to the character correspondence signals; said identifying step including forming a set of signals representative of the corresponding of the input character string to said predetermined groups responsive to the character correspondence signals; and selecting the stored reference character set most closely corresponding to the input character string jointly responsive to the character correspondence signals, the reference character sets and the group correspondence signals.
21. A method for recognizing a string of spoken characters comprising the steps of: storing a plurality of reference character sets in predetermined groups; generating a set of signals representative of the acoustic features of spoken reference characters; generating a signal representative of the acoustic features of each spoken input characters; producing a set of signals representative of the acoustic correspondence of the input characters to said reference characters jointly responsive to the input character acoustic feature signals and the reference character acoustic feature signals; and identifying the input character string as one of the stored reference character sets responsive to the character correspondence signals; said identifying step including forming a set of signals representative of the corresponding of the input character string to said predetermined groups responsive to the character correspondence signals; and selecting the stored reference character set most closely corresponding to the input character string jointly responsive to the character correspondence signals, the reference character sets and the group correspondence signals. 22. A method for recognizing a string of spoken characters according to claim 21 wherein said reference character set selecting step comprises searching the groups in order of most to least correspondence to the input character string including selecting the unsearched group having the closest correspondence to the input character string; forming a correspondence signal for each reference character set in the selected group responsive to the reference character sets of the selected group and the character correspondence signals; selecting the reference character set having the closest correspondence to the input character string responsive to the selected group reference character set correspondence signals; and identifying the input character string as the selected reference character set responsive to the correspondence signal of the reference character set having closer correspondence to the input character string than the correspondence signals of the unsearched groups.