squared error between the input speech and the synthesized speech in the fixed codebook search the fixed codebook search is executed sub frame by sub frame the fixed codebook is composed of a plurality of codewords and a codeword includes several representative samples in the sub frame the most adequate codeword which can express the speech signal is searched in the codebook during the fixed codebook search for example in accordance with the g 729a codec the sub frame is composed of 40 samples and one codeword includes 4 samples therefore 4 samples that best represent the 40 samples are searched during the fixed codebook search of the g 729a codec the well known fixed codebook searching methods are the full search method the focused search method and the depth first tree search method as mentioned in the description of the related art also the least significant pulse replacement method is disclosed lately the present invention suggests a global pulse replacement method by overcoming the problem of the least significant pulse replacement method the global pulse replacement method is explained as follows the present invention is applied to the celp speech coding system and a preferred embodiment of the present invention is based upon amr nb 12 2 kbps mode a codebook vector that maximizes a value of eq 1 is chosen in each fixed codebook search max k ue89e ue89e q k max k ue89e c k 2 e k max k ue89e d t ue89e c k 2 c k t ue89e u03c6 ue89e ue89e c k eq ue89e 1 a k th codebook vector is described as c k and t denotes a transposed matix a correlation vector d and a matrix u03c6 are described as d ue8a0.