7 Half rate Voice Activity Detection (VAD)

06.023GPPHalf rate speech processing functionsTS

The half rate VAD function is described in GSM 06.42 [8].

The input to the VAD is a set of parameters computed by the half‑rate speech encoder defined in GSM 06.20 [4]. The VAD uses this information to decide whether each 20 ms speech coder frame contains speech or not.

NOTE: The VAD flag is an input to TX DTX handler and does not control the transmitter keying directly.

GSM 06.42 [8] describes the VAD algorithm and GSM 06.06 [11] defines the C code. The verification of compliance to GSM 06.42 [8] is achieved by use of digital test sequences (see GSM 06.07 [10]) applied to the same interface as the test sequences for the speech codec.