Improving the performance of CELP-based speech coding at low bit rates

The authors review the CELP (code excited linear prediction) coding algorithm, and the efforts recently made for improving the performance and reducing the complexity. The efforts for improving the coding performance have been aimed not only at making the quality better, but also at further reducing the bit rate without degrading the quality. A sparse-delta codebook is introduced as an example of a codebook with a computationally efficient structure. Multimode coding is then described for improving the perceptual quality of CELP at low bit rates