7 Half rate Voice Activity Detection (VAD)
3GPP46.002Half rate speechHalf rate speech processing functionsRelease 17TS
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.