Daniel Lin

Method and device for encoding speech using open-loop pitch analysis

The present invention is a synthetic speech encoding device that produces a synthetic speech signal which closely matches an actual speech signal. The actual speech signal is digitized, and excitation pulses are selected by minimizing the error between the actual and synthetic speech signals. The preferred pattern of excitation pulses needed to produce the synthetic speech signal is obtained by using an excitation pattern containing a multiplicity of weighted pulses at timed positions. The selection of the location and amplitude of each excitation pulse is obtained by minimizing an error criterion between the synthetic speech signal and the actual speech signal. The error criterion function incorporates a perceptual weighting filter which shapes the error spectrum.

LPC vector quantization based on critical‐band analysis

Critical‐band spectrum is known to represent the redundancies of the human auditory system. Vector quantization constitutes a minimal redundant code set for a given signal source. In this study, these techniques are combined in a low‐rate speech analysis/resynthesis system. An important design criterion for a perceptually based source coder is to define an appropriate mapping between the analysis codebook in critical‐band domain and the synthesis codebook in LPC domain. Several methods for generating and searching the synthesis codebooks based on the perceptual distance criterion are proposed. Their performance with other LPC‐based distance measures (e.g., log area, LSP, cepstral) is compared. These results indicate a substantial improvement in the quality of synthetic speech for the perception‐based system due to smoother spectral trajectories in the low‐frequency regions.