06.073GPPHalf Rate Speech: Test Sequence for GSM Half Rate Speech CodecTS

This clause describes the test sequences designed to exercise the GSM half rate speech transcoder (GSM 06.20 [2]).

6.1 Codec configuration

The speech encoder shall be configured to operate in the non‑DTX mode. The VAD and SP flags shall be set to 1 at the speech encoder output.

6.2 Speech codec test sequences

Table 5 lists the location and size of the speech codec test sequences.

6.2.1 Speech encoder test sequences

Three encoder input sequences are provided:

‑ SEQ01.INP ‑ Sequence for exercising the LPC vector quantization codebooks;

‑ SEQ02.INP ‑ Sequence for exercising the long term predictor codebooks;

‑ SEQ03.INP ‑ Sequence for exercising the remaining excitation codebooks.

The SEQ01.INP sequence causes the GSM half rate speech encoder to select every vector in the three reflection coefficient vector quantizers at least once. In a correct implementation, the resulting speech encoder output parameters shall be identical to those specified in the SEQ01.COD sequence.

The SEQ02.INP sequence causes the encoder to select at least once every quantization level in the eight bit table of long term filter lags for the first subframe, and every quantization level in the four bit delta lag quantizer for subframes 2, 3, and 4. In a correct implementation, the resulting speech encoder output parameters shall be identical to those specified in the SEQ02.COD sequence.

The SEQ03.INP sequence causes the encoder to select each of the quantization levels at least once for the remaining GSM half rate speech coder parameters: R0 (frame energy), the soft interpolation decision for the LPC coefficients, the four voicing modes, the gain vectors (GSP0) for each of the voicing modes, and the voiced and unvoiced VSELP codebooks. The only exception to this is that two GSP0 levels in the unvoiced mode are not selected. However, these levels are exercised in the GSM half rate speech decoder as described below. In a correct implementation, the resulting speech encoder output parameters shall be identical to those specified in the SEQ03.COD sequence.

6.2.2 Speech decoder test sequences

Four speech decoder input sequences are provided:

‑ SEQ01.DEC;

‑ SEQ02.DEC;

‑ SEQ03.DEC;

‑ SEQ04.DEC.

The SEQ01.DEC, SEQ02.DEC, and SEQ03.DEC sequences test the operation of the GSM half rate speech decoder in the absence of channel errors. They are derived from the corresponding SEQXX.INP sequences. In a correct implementation, the resulting speech decoder output shall be identical to the SEQ01.OUT, SEQ02.OUT, and SEQ03.OUT sequences, respectively. Together, these three sequences exercise every quantization level in every codebook in the decoder, with the exception of two GSP0 levels in the unvoiced mode.

The SEQ04.DEC sequence is designed to test the GSM half rate speech decoder under conditions which can result from channel errors. In particular, it is the decoding of LTP lags at the lag table boundaries, given delta lag codes which if incorrectly decoded would point outside the eight bit lag table, that is being tested. Also, the two remaining GSP0 levels in the unvoiced mode are exercised by this sequence. In a correct implementation, the resulting speech decoder output shall be identical to the SEQ04.OUT sequence.

6.2.3 Codec homing sequence

In addition to the test sequences described above, two homing sequences are provided to assist in codec type approval testing. SEQ05.INP contains one encoder‑homing‑frame. SEQ05.DEC contains one decoder‑homing‑frame. The use of these sequences is described in GSM 06.02 [8].

Table 5: Location and size of speech codec test sequences