Patent ID: 7657429

Claim:
A coding apparatus for coding a digital signal with reference to a codebook, comprising: a holding unit operable to hold a first codebook and at least one second codebook; a scaling unit operable to scale inputted signal values so that the signal values fall within a predetermined range of values including N, N being a natural number, consecutive integers; a quantizing unit operable to quantize the scaled signal values respectively into digital signal values within a range of values of the N integers; a coding unit operable to replace a digital signal with codes with reference to either the first codebook or the at least one second codebook held in said holding unit, corresponding to a set of the quantized digital signal values quantized by said quantizing unit; and a selecting unit operable to select another codebook, which said coding unit is to refer to, of different quantization resolution, from among either the first codebook or the at least one second codebook depending on a set of the quantized signal values quantized by said quantizing unit, wherein the first codebook shows one-to-one correspondence between N codes and the N integers, the at least one second codebook shows one-to-one correspondence between M, M is a natural number less than N, codes and M integers which are a subset of the N integers, the at least one second codebook having quantization resolution lower than quantization resolution of the first codebook, and said coding unit refers to, even when switching the codebook being referred to based on the codebook selected by the selecting unit, the codebook using the same integer values which are indicated by the quantized digital signal quantized by said quantization unit, and replaces the integer values which are indicated by the quantized digital signal with codes with reference to the selected codebook.