Toll-quality speech coding at 8 kbs

There has been an ongoing effort to achieve very high quality speech coding at medium transmission bit rates. Consequently, the TIA has chosen the Vector SUM Linear Predictive (VSELP) implementation of an 8 kb/s coder to be the standard for North-American cellular digital telephony. However, it was only recently that, in view of the increased research focus on developing toll-quality speech coding at such bit rates, the CCITT has imposed a set of specifications for standardizing low-delay coders operating at 8 kb/s. The Low-Delay Code Excited Linear Predictive (LD-CELP) suggested by Chen is presently the only potential candidate for CCITT standardization, achieving a one-way coding delay of 10 ms. However, just like the VSELP coding algorithm, the 8 kb/s LD-CELP version does not quite yield toll-quality reconstructed speech. The purpose of the work in this thesis is to establish the minimum requirements for a coding structure capable of generating toll-quality coded speech at 8 kb/s. The purpose of this thesis is to show that, by slightly relaxing the coding delay constraint, perceptual enhancement techniques yield toll quality coding after redesigning and fine-tuning the optimization and quantization procedures of a CELP coder