Variable-rate low-delay analysis-by-synthesis speech coding at 8-16 kb/s

The authors report results on lattice low delay vector excitation coding (LLD-VXC) for rates in the range of 8-16 kb/s. The LLD-VXC, which is based on a backward adaptive analysis-by-synthesis configuration, an adaptive lattice short-term predictor, an adaptive lattice perceptual weighting filter, and an adaptive pitch predictor, offers toll speech quality at 16 kb/s with moderate complexity and a total communication delay of under 2 ms. For bit rates below 16 kb/s, the LLD-VXC keeps the same basic structures and algorithms but uses different code-vector dimensions and codebook sizes to achieve different bit rates. For reducing computational complexity, the sign-error-sign-data least mean square adaptive lattice algorithm was derived and implemented in LLD-VXC. The sign algorithm significantly reduced computational complexity at the expense of a slight speech quality degradation