Wideband speech codec using a higher sampling rate in analysis and synthesis filtering than in excitation searching

Abstract

A codec (coder and decoder) in which LP analysis and LP synthesis of a full wideband speech signal is performed, and, in an excitation search part of the coder (searching for a codeword in case of CELP), the signal is divided into a lower band and a higher band with the lower band searched using a decimated target signal obtained by decimating the input speech signal after filtering it through a wideband LP analysis filter. White noise is optionally used for the higher band excitation. In the decoder, the lower band excitation is first interpolated, and then the two excitations (lower band and higher band) are added together and filtered through a wideband LP synthesis filter. Thus, an LP encoding is provided in which the sampling rate used for the search for a lower band excitation is less than the wideband sampling rate used in the LP analysis and synthesis.