Global variance modeling on frequency domain delta LSP for HMM-based speech synthesis

The speech parameter generation algorithm considering global variance (GV) for HMM-based speech synthesis proved to be effective against the over-smoothing problem. However, the correlation between dimensions of parameter vector is not sufficiently considered in the current GV model. For some parameters, e.g., Line Spectral Pairs (LSP), the difference of adjacent LSPs has strong influence on the spectral envelope. Considering this important feature, the paper proposes a GV modeling on the difference of adjacent LSPs, i.e., GV on frequency domain delta LSP. By improving the GV likelihood on frequency domain delta LSP, the over-smoothing effect of generated parameter trajectory is better alleviated than conventional one. The result of a perceptual evaluation shows the proposed method outperforms the conventional one, and the naturalness of synthetic speech is improved.