BACKWARD ADAPTIVE LATTICE AND TRANSVERSAL PREDICTORS IN LOW-DELAY CELP CODERS

This paper examines several backward lattice and transversal algorithm s for updating the short-term prediction filter and the weighting filt er in low-delay CELP (LD-CELP) systems operating at 16 kbit/s. We have considered block recursive adaptation structures and evaluated their relative merits both in terms of reconstructed speech quality and comp utational complexity. Comparisons in terms of performance are based on objective measures (signal-to-noise ratio, segmental signal-to-noise ratio and a frequency weighted signal-to-noise ratio) and on subjectiv e results obtained from listening tests. Simulation results are presen ted and discussed for both ideal and noisy communication channels. Amo ng the investigated adaptation schemes, the best performance in error- free channel was obtained with the exponential window lattice and the signal-driven lattice. However, a trade-off among robustness in noisy channels, performance under error-free conditions and computational co mplexity leads to the residual-drive lattice as an attractive algorith m to be used in LD-CELP structures.