A Novel HMM-Based TTS System using Both Continuous HMMS and Discrete HMMS

The conventional HMM-based speech synthesis system (HTS) has encountered two over-smoothing problems in both time domain and frequency domain. To resolve the two problems, the paper presents a new HTS framework using both continuous HMMs and discrete HMMs. By the replacement of spectral envelope represented by continuous Gaussian distribution with that represented by discrete codevector, the over-smoothing problem in frequency domain can be resolved, and by the replacement of the parameter generation algorithm using dynamic features with a new well-designed codevector selection algorithm, the over-smoothing problem in time domain can also be better resolved. Experimental results show that the using of both continuous HMMs and discrete HMMs significantly improves the voice quality of synthesized speech.