Algorithm compatible improvements for FS-1016 CELP

Federal Standard 1016 CELP is a widely adopted standard for speech coding at 4.8 kbps. In this paper we address the issue of improving the existing standard using techniques maintaining compatibility and interoperability. Two techniques are discussed, selective harmonic pre-emphasis and delayed decision parameter estimation. Selective harmonic pre-emphasis is applied in the analysis-by-synthesis loop of the analyzer to strengthen the harmonic structure in both voiced and mixed areas. Delayed decision is also applied in the analysis-by-synthesis loop of the analyzer for improving the performance of the adaptive codebook. Informal and formal results of each algorithm modification demonstrate improvement.