QR FACTORIZATION IN THE CELP CODER

In most recently proposed speech coders at bit rates between 4.8 and 16 kbit/s, the synthetic speech signal is obtained by filtering a synthetic excitation signal through an all-pole filter, that models the vocal tract spectral characteristics. Defining the excitation signal has been, and still is, an active field of research. Multipulse coders, CELP coders, regular-pulse coders , etc … have been quite successful and they basically differ by the structure of their excitation. These coders usually include a long-term predictor, which can be seen as an adaptive codebook containing past excitation. In a general way, the excitation vector e may be modeled as a linear combination of K signals, originated from K codebooks and multiplied by K associated gains