1. A method of converting a linear predictive coding (LPC) coefficient into a coefficient having order characteristics and quantizing the coefficient, the method comprising: splitting a vector of the coefficient having the order characteristics into a plurality of subvectors; selecting a codebook in which an available bit is allocated to each of the subvectors according to a distribution of elements of each of the subvectors; and quantizing, performed by using at least one processor, each of the subvectors using the selected codebook and generating a codebook index of each of the subvectors, wherein a different available bit is allocated to subvectors in each of a plurality of normalized codebooks for use in quantizing lower subvectors, according to a distribution of elements of the subvectors.