Subband synthesized LPC vector quantization (SBS-LPC-VQ)

This paper presents a new LPC parameter quantization method-SubBand Synthesized LPC Vector Quantization (SBS-LPC-VQ). In the subband synthesis process, the relationships between subband spectra and whole band LPC spectrum are established and thus the vector quantized subband LPC parameters are mapped to the whole band LPC parameters. This new SBS-LPC-VQ method overcomes high complexity problem of vector quantization of LPC parameters and isolates the distortion within each subband during the VQ process. It also provides the flexibility of assigning the bits to be used for each subband, choosing the order for LPC filter and determining the number of bands for the subband classification. The Critical band Weighting Spectral Distortion Measure (CW-SDM), which is a perceptually motivated objective measure by using a critical band weighting function, is used for measuring the distortion of quantized LPC spectrum. Using this kind of distortion measure, the experiments show that the SBS-LPC-VQ has obtained 24 bits/frame for coding whole 16th order LPC parameters with about 1 dB average spectral distortion. For comparison, the results by conventional spectral distortion measure (SDM) are also presented in the paper.