Beyond Multi-Pulse and CELP: Towards High Quality Speech at 4 kb/s

In recent years, rapid progress has been made in producing high quality speech at low bit rates. The present generation of speech coders, using either multi-pulse or codebook excitation, are able to generate speech of reasonably good quality at bit rates as low as 4.8 kb/s. The progress in speech coding is leading to new standards for secure voice communication at 4.8 kb/s and for digital cellular radio. With the move to establish these standards, new initiatives are needed in speech coding research to push the frontiers for high quality speech coding even lower - down to 2. 4 kb/s. High speech quality at such low bit rates cannot be achieved by incremental improvements of the existing multi-pulse and CELP concepts.