The transcoding procedure specified in this ETS is applicable for the enhanced full rate traffic channel (TCH) in the GSM system. In GSM EFR 06.51, a reference configuration for the speech transmission chain of the GSM EFR 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 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. In the receive direction, the inverse operations take place. This draft European Technical Specification (ETS) describes the detailed mapping between input blocks of 160 speech samples in 13-bit uniform PCM format to encoded blocks of 260 bits and from encoded blocks of 260 bits to output blocks of 160 reconstructed speech samples. The sampling rate is 8000 sample/s leading to a bit rate for the encoded bit stream of 13 kbit/s. The coding scheme is the so-called Algebraic Code Excited Linear Prediction Coder, here-after referred to as ACELP. This ETS also specifies the conversion between A-law PCM and 13-bit uniform PCM. Performance requirements for the audio input and output parts are included only to the extent that they affect the transcoder performance. This part also describes the codec down to the bit level, thus enabling the verification of compliance to the part to a high degree of confidence by use of a set of digital test sequences. These test sequences are also described and are available on disks.