Patent ID: 7363220

Claim:
A speech decoding method according to code-excited linear prediction (CELP) wherein the speech decoding method receives a coded speech including a linear prediction parameter code, an adaptive code, and a gain code, and generates an excitation signal by using an excitation code vector and an adaptive code vector and synthesizes a speech by using the excitation signal, the speech decoding method comprising: decoding the gain code from the coded speech; obtaining the adaptive code vector from an adaptive codebook; processing the decoded gain code in order to classify the decoded gain code as being one of a plurality of gain codes, the plurality of gain codes including a first gain code corresponding to a first noise level and a second gain code corresponding to a second noise level, the second noise level being greater than the first noise level; obtaining based on an excitation codebook a first time series vector as the excitation code vector if the decoded gain code is classified as being the first gain code; obtaining based on an excitation codebook a second time series vector as the excitation code vector if the decoded gain code is classified as being the second gain code, the second time series vector having a greater noise level than the first time series vector; generating the excitation signal by using the excitation code vector and the adaptive code vector; and synthesizing the speech by using the excitation signal.