The present document describes the detailed mapping from input blocks of 160 speech samples in 13-bit uniform PCM format to encoded blocks of 95@ 103@ 118@ 134@ 148@ 159@ 204@ and 244 bits and from encoded blocks of 95@ 103@ 118@ 134@ 148@ 159@ 204@ and 244 bits to output blocks of 160 reconstructed speech samples. The sampling rate is 8 000 samples/s leading to a bit rate for the encoded bit stream of 4.75@ 5.15@ 5.90@ 6.70@ 7.40@ 7.95@ 10.2 or 12.2 kbit/s. The coding scheme for the multi-rate coding modes is the so-called Algebraic Code Excited Linear Prediction Coder@ hereafter referred to as ACELP. The multi-rate ACELP coder is referred to as MR-ACELP. In the case of discrepancy between the requirements described in the present document and the fixed point computational description (ANSI-C code) of these requirements contained in GSM 06.73 [6]@ the description in GSM 06.73 [6] will prevail. The ANSI-C code is not described in the present document@ see GSM 06.73 [6] for a description of the ANSI-C code. The transcoding procedure specified in the present document is applicable for the adaptive multi-rate full rate and half rate speech traffic channels (TCH) in the GSM system. In GSM 06.71 [5]@ a reference configuration for the speech transmission chain of the GSM adaptive multi-rate (AMR) system is shown. According to this reference configuration@ the speech encoder takes its input as a 13-bit uniform PCM signal either from the audio part of the Mobile Station or on the network side@ from the PSTN via an 8-bit A-law or ??-law to 13-bit uniform PCM conversion. The encoded speech at the output of the speech encoder is delivered to a channel encoder unit which is specified in GSM 05.03 [3]. In the receive direction@ the inverse operations take place.