New Annex F introduced by Ammendment 7 of ITU-T G.729.1 describes the voice activity detector (VAD) to be used together with the DTX/CNG scheme of Annex C to provide the complete functionality of an ITU-T G.729.1 discontinuous transmission system. Since the VAD algorithm described in Annex F is the same as in ITU-T G.720.1 Annex A, this annex makes reference to ITU‑T G.720.1 Annex A for the parts of the description that are identical to the original Recommendation.

The ANSI C source code in the electronic attachment to this text is an integral part of Annex F.