1 General

06.323GPPTSVoice Activity Detection (VAD)

The function of the VAD is to indicate whether each 20 ms frame produced by the speech encoder contains speech or not. The output is a binary flag which is used by the TX DTX handler defined in GSM 06.31 [4].

The ETS is organized as follows.

Clause 2 describes the principles of operation of the VAD.

In clause 3, the computational details necessary for the fixed point implementation of the VAD algorithm are given. This clause uses the same notation as used for computational details in GSM 06.10.

The verification of the VAD is based on the use of digital test sequences. Clause 4 defines the input and output signals and the test configuration, whereas the detailed description of the test sequences is contained in clause A.2.

The performance of the VAD algorithm is characterized by the amount of audible speech clipping it introduces and the percentage activity it indicates. These characteristics for the VAD defined in the present document have been established by extensive testing under a wide range of operating conditions. The results are summarized in clause A.3.