The present document describes the detailed mapping between input blocks of 160 speech samples in 13-bit uniform
PCM format to encoded blocks of 244 bits and from encoded blocks of 244 bits to output blocks of 160 reconstructed
speech samples. The sampling rate is 8 000 sample/s leading to a bit rate for the encoded bit stream of 12,2 kbit/s. The
coding scheme is the so-called Algebraic Code Excited Linear Prediction Coder, hereafter referred to as ACELP.
This EN 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 described in GSM 06.54 [7] and are
available on disks.
In case of discrepancy between the requirements described in this EN and the fixed point computational description
(ANSI-C code) of these requirements contained in GSM 06.53 [6], the description in GSM 06.53 [6] will prevail.
The transcoding procedure specified in this EN is applicable for the enhanced full rate speech traffic channel (TCH) in
the GSM system.
In GSM 06.51 [5], a reference configuration for the speech transmission chain of the GSM enhanced full rate (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 [3]. In the receive direction, the inverse operations take place.
PUBLISHED
SSH EN 301 245 V4.1.1:2000
60.60
Standard published
13 shk 2017
English