Lattice low-delay vector excitation coding of speech at 8-16 kb/s

Lattice low-delay vector excitation coding (LLD-VXC) is a speech coding system based on analysis-bysynthesis excitation coding and backward adaptation of the synthesis filter. The introduction of a lattice filter as a (high order) short-term predictor has significant advantages, such as fast tracking of speech signal nonstationarities, simple stability verification, and uniform distribution of the computational load. The objective of this paper is to present a Lattice LD-VXC (LLD-VXC) codec and experimental results obtained at rates of 8, 9.6, and 16 kb/s. A sign algorithm for lattice filter adaptation is introduced in order to reduce computational complexity. An LLD-VXC codec with a 20th-order lattice predictor, a 10thorder lattice weighting filter, and a backward pitch predictor achieved toll quality at 16 kb/s and good communications quality at 8-9.6 kb/s with a delay of less than 2 ms and reasonable complexity.