06.323GPPTSVoice Activity Detection (VAD)
This clause provides information on the digital test sequences that have been designed to help the verification of implementations of the Voice Activity Detector. Copies of these sequences are available (see clause A.2).
4.1 Test configuration
The VAD must be tested in conjunction with the speech encoder defined in GSM 06.10. The test configuration is shown in figure 4.1. The input signal to the speech encoder is the sop[…] signal as defined in GSM 06.10 table 5.1. The relevant parameters produced by the speech encoder are input to the VAD algorithm to produce the VAD output. This output has to be checked against some reference files.
The file format of the encoder output parameters given in GSM 06.10 table 5.1 is extended to carry the VAD information.
The VAD information is placed in the unused bit 15 (MSB) of the first encoded parameter:
LAR(1): bit 15 = 1 if VAD on
bit 15 = 0 if VAD 0ff
Furthermore, in order to facilitate approval testing over the air interface, the SP flag generated by the TX DTX handler (see GSM 06.31) on the basis of the VAD flag is placed in the MSB position of the second encoded parameter:
LAR(2): bit 15 = 1 if SP on
bit 15 = 0 if SP off
The output file will also contain the SID codeword and the comfort noise parameters as described in GSM 06.12 and GSM 06.31.
Figure 4.1: VAD test configuration
4.2 Test sequences
The test sequences are described in detail in clause A.2.
Annex A (informative):