Quantization of the LPC model with the reconstruction error distortion measure

In Linear Predictive Coding algorithms, the coding of the speech signal consists of two separate stages: coding of the LPC model and coding of the excitation. In CELP, the LPC excitation is coded by Analysis-by-Synthesis in the reconstruction domain, not by minimization of the error in the LPC residual domain. Commonly used distortion measures for quantization of the LPC spectral model are the Spectral Distortion and the Likelihood Ratio. For small quantization errors, they belong to a class of similar distortion measures which express an error in the residual domain. A new spectral distortion measure is proposed, the Reconstruction Error Distortion measure, which expresses an error in the reconstruction domain. Preliminary results indicate that about five bits per frame can be gained with this new measure, without a loss in subjective quality.