scope:

The transcoding procedure specified in this recommendation is applicable for the full-rate traffic channel (TCH) in the Pan-European Digital Mobile Radio (DMR) system. The use of this transcoding scheme for other applications has not been considered.

In recommendation GSM 06.01, a reference configuration for the speech transmission chain of the digital cellular telecommunications 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 Rec.GSM 05.03. In the receive direction, the inverse operations take place.

This recommendation 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 an average bit rate for the encoded bit stream of 13 kbit/s. The coding scheme is the so-called Regular Pulse Excitation - Long Term prediction - Linear Predictive Coder, here-after referred to as RPE-LTP.

This recommendation 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. The recommendation also describes the codec down to the bit level, thus enabling the verification of compliance to the recommendation 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 floppy disks.