A new set of context labels was developed for HMM-based speech synthesis of Japanese. The conventional labels include those directly related to sentence length, such as number of "mora" and order of breath group in a sentence. When reading a sentence, it is unlikely that we count its total length before utterance. Also a set of increased number of labels is required to handle sentences with various lengths, resulting in a less efficient clustering process. Furthermore, labels related to prosody are mostly designed based on the unit "accent phrase," whose definition is somewhat unclear; it is not uniquely defined for a given sentence, but also is affected by other factors such as speaker identity, speaking rate, and utterance style. Accent phrase boundaries may be labeled differently for utterances of the same content, and this situation affects other labels, because of numerical labeling scheme counted from the sentence/breath-group initial. In the proposed labels, "bunsetsu" is used instead. Also, we only view its relations with preceding and following "bunsetsu’s." Thus labels not related to the sentence lengths are obtained, with easier automatic prediction only from sentence representations. Validity of the proposed labels was shown through speech synthesis experiments.

Index Terms: speech synthesis, context labels, linguistic information