Interpolating the history improved excitation coding for high quality CELP coding
P. Hedelin, Thomas Eriksson · 2002
A procedure is presented where the conventional innovation codebook approach of CELP coding is replaced by an interpolative scheme. A generalized LTP-codebook constitutes the basis for the interpolation. A pre-requisite to efficient interpolation concerns establishing the neighboring vectors of a given LTP entry. We discuss several working approximations for establishing a suitable neighborhood concept. By simulations we have found that the interpolative scheme leads to 17-20 bits for the excitation coding of one block. In addition to this, some 3-4 bits are required for block gain. A standard CELP typically spends 25 bits or more for one block of excitation coding. The subjective quality of our proposed coding scheme compares favorably with standard CELP. In particular, the interpolation improves the pitch-related properties giving a less noisy subjective impression.