06.013GPPFull Rate Speech Processing FunctionsTS
The input to the VAD is a set of parameters computed by the full‑rate speech encoder defined in GSM 06.10 . The VAD uses this information to decide whether each 20 ms speech coder frame contains speech or not. Note that the VAD flag is an input to TX DTX handler and does not control the transmitter keying directly.
The technical specification describes the VAD algorithm down to the bit level. The conventions used in the bit‑exact specification are the same as those used in GSM 06.10 . The verification of compliance to the technical specification is achieved by use of digital test sequences applied to the same interface as the test sequences for the speech codec. These test sequences are also described and are available on floppy disks.