Scalable speech coding spanning the 4 Kbps divide

This paper examines a scalable method for coding the LP residual. The scalable method is capable of increasing the accuracy of the reconstructed speech from a parametric representation at low rates to a more accurate waveform matched representation at higher rates. The method entails pitch length segmentation, decomposition into pulsed and noise components and modeling of the pulsed components using a fixed shape pulse model in a closed-loop, Analysis by Synthesis system. Subjective testing is presented that indicates that in addition to the AbyS modeling, the pulse parameter evolution must be constrained in synthesis. Results indicate that this proposed method is capable of producing perceptually scalable speech quality as the bit rate is increased through 4 kbps.