A Fast Adaptive-codebook Search Algorithm for G.723.1 Speech Coder

This letter presents a new fast search algorithm for the multitap adaptive codebook used in the G.723.1 standard speech coder. In contrast with the standard method that a closed-loop pitch lag and gains for a fifth-order pitch predictor are searched simultaneously, the proposed algorithm adopts a sequential and restricted approach to determine the parameters. In other words, the proposed scheme first determines a couple of pitch lag candidates using a first-order pitch predictor and then computes the pitch gains of the fifth-order predictor within a restricted search area. Experimental results confirm that the proposed algorithm reduces the total complexity by 30.69% in the encoding process and provides speech quality equivalent to the standard method.