Speech coding using efficient block codes

Digital coders invariably introduce errors into analog signals such as speech. The importance of adjusting the spectrum of the error so as to minimize the subjective distortion is now well recognized. The optimum noise spectrum for minimum subjective distortion is in general non-flat. Predictive coders use instantaneous quantizers with feedback around the quantizer to shape the quantizing noise spectrum. However, for non-flat spectra, instantaneous quantizers are suboptimal. We have therefore considered and reported on non-instantaneous digital speech coders using tree-search procedures to determine the optimal innovation sequence. In this paper, we describe tree-search procedures to determine optimal block codes. We discuss both random and special block codes based on optimum packing of Voronoi regions on unit spheres in multi-dimensional spaces.