Unit selection algorithm for Japanese speech synthesis based on both phoneme unit and diphone unit

This paper proposes a novel unit selection algorithm for Japanese Text-To-Speech (TTS) systems. Since Japanese syllables consist of CV (C: Consonant, V: Vowel) or V, except when a vowel is devoiced, CV units are basic to concatenative TTS systems for Japanese. However, speech synthesized with CV units sometimes have discontinuities due to V-V concatenation; In order to alleviate such discontinuities, longer units (CV* or non-uniform units) have been proposed. However, the concatenation between V and V is still unavoidable. To address this problem, we propose a novel unit selection algorithm that incorporates not only phoneme units but also diphone units. The concatenation in the proposed algorithm is performed at the vowel center as well as at the phoneme boundary. Results of evaluation experiments clarify that the proposed algorithm outperforms the conventional algorithm.