Determination of an excitation vector in a CELP coder

摘要

The determination method involves using an optimum vector (Copt) from a subset of excitation vectors suitable for maximising a given criterion. These vectors have component values +1 and -1 corresponding to an excitation sample sequence of a linear prediction filter. The criterion is given by the square of the ratio of the scalar product of the excitation vector with the target vector (T) to the modulus of the excitation vector after being passed through a direct linear prediction filter. The filtering process involves preselecting an excitation vector (CO) with components having the same sign as the samples corresponding to the target vector, or having the inverse sign. If the selected vector does not belong to the subset, a vector is selected from the subset (CO'-CN') which maximises the given criterion and those nearest to it in the full set (C1-CN).