Patent ID: 8249860

Claim:
An adaptive excitation vector quantization apparatus that receives, as an input, linear prediction residual vectors of a length m and linear prediction coefficients generated by dividing a frame of a length n into a plurality of subframes of the length m and performing a linear prediction analysis where the length n and the length m are integers, and that performs adaptive excitation vector quantization per subframe using more bits in a first subframe than in a second subframe, the apparatus comprising: an adaptive excitation vector generator including at least one of at least one processor and at least one circuit that cuts out an adaptive excitation vector of an adaptively changed length r from an adaptive excitation codebook, the length r being greater than the length m and at most equal to the length n; a target vector generator including at least one of the at least one processor and the at least one circuit that generates a target vector of the length r from the linear prediction residual vectors of the plurality of subframes; a synthesis filter including at least one of the at least one processor and the at least one circuit that generates a r×r impulse response matrix using the linear prediction coefficients of the plurality of subframes; an evaluation measure calculator including at least one of the at least one processor and the at least one circuit that calculates evaluation measures of adaptive excitation vector quantization with respect to a plurality of pitch period candidates, using the adaptive excitation vector of the length r, the target vector of the length r and the r×r impulse response matrix; and an evaluation measure comparator including at least one of the at least one processor and the at least one circuit that compares the evaluation measures with respect to the plurality of pitch period candidates and finds a pitch period of a highest evaluation measure as a result of the adaptive excitation vector quantization of the first subframe, wherein, when a difference is larger between a first number of bits involved in the adaptive excitation vector quantization of the first subframe and a second number of bits involved in the adaptive excitation vector quantization of the second subframe, the length r is set longer.