Evaluation of LPC/CVSD tandem connections

The purpose of this study was to assess the effects of LPC/CVSD tandem connections and to investigate ways of improving performance. In the case of the CVSD-to-LPC connection, the CVSD quantizing noise severely affects the estimate of LPC coefficients, thereby distorting the spectral representation. An averaging technique was shown to reduce the average spectral distance from the noiseless case; however, no statistically significant perceptual advantage was measured. In the LPC-to-CVSD connection, it was found that modest improvements can be measured both in signal-to-noise ratio and perceptually, by modifying the phase in LPC synthetic speech before CVSD coding.