Method of determining an acoustic model for a word

Abstract

For the recognition of spoken text it is necessary that the words to be recognized are available in acoustically modeled form, i.e. in the form of a sequence of reference values. These reference values are determined from a known, spoken text during a training phase, in that from this text there are derived characteristic values at regular intervals, as during the recognition, which characteristic values are arranged according to triphones so as to form groups or so-called clusters. These groups constitute the basis for the reference values. In the case of a recognition system involving a very large vocabulary, however, not all triphones will occur during the training phase, unless the text is prohibitively long. In order to enable the reference values to be determined also for words containing triphones which have not occurred, such a triphone must be associated with an available group. To this end, all groups are examined so as to determine whether they have the same central phoneme in interrelationship with either the left-hand or the right-hand phoneme as the triphone to be associated. The group for which this is most often the case is selected as the associated group. The vast majority of words can thus be modeled on the basis of triphones. Modifications of this rule are described for words containing triphones which cannot be directly associated in this manner.