HMM-based emphatic speech synthesis for corrective feedback in computer-aided pronunciation training

This paper investigates the incorporation of hidden Markov model (HMM) based emphatic speech synthesis for audio exaggeration into an audio-visual speech synthesis framework for the corrective feedback in computer-aided pronunciation training (CAPT). To improve the voice quality of the synthetic emphatic speech, this paper proposes a new method for HMM training. In this method, the contextual questions for decision tree building are extended by considering the emphasis-related information. HMMs are then trained using a small scale emphatic corpus together with a large scale neutral corpus. The emphatic corpus is used to ensure the quality of the emphatic speech segments whereas the neutral corpus is to further improve the quality of both the non-emphatic speech segments and the emphatic ones. Finally, emphatic speech synthesis is achieved by extending the Flite+hts_engine. Experimental results show that our method can synthesize emphatic speech with high quality and make the feedback more discriminatively perceptible.