Phase modeling and quantization for low-rate harmonic+noise coding

This paper presents a novel technique for modeling and quantization of the phase information in low-rate harmonic+noise coding. In the proposed phase model, each frequency track is adjusted by a frequency deviation (FD) that reduces the error between measured and predicted phases. By exploiting the intraframe relationship of the FD's, the phase information is represented more efficiently when compared with the representation by measured phases or by phase prediction residuals. An efficient FD quantization scheme based on closed-loop analysis is also developed. In this scheme, the FD of the first harmonic and a vector of the FD differences are quantized by minimizing a perceptually weighted distortion measure between the measured phases and the quantized phases. The proposed technique reproduces the temporal events of the original speech signal and improves the subjective quality of the synthesized speech using 13 bits per frame only.