This appendix deals with optimization of the VAD, described in Annex B, in conjunction with the main body of ITU-T Rec. G.729, and ITU-T Rec. G.729 Annexes A, C or H, when used for VoIP applications.

This appendix addresses in particular the following problems:

1) Undesired performance for input signals with signal-to-noise (SNR) levels below 15 dB;

2) Annoying breathing-like noise in CNG phase;

3) VAD performance under heavy noise condition;

4) Wrong variable initialization.

The use of this appendix is intended for VoIP systems where overall quality is considered as more important than optimization of the bandwidth.

This appendix contains two electronic attachments. One consists of the modified source C code file for vad.c (of Annex B/G.729). The other is a set of test files that were used to test the algorithm in this appendix.