4.3.7 VAD Decision

26.0943GPPAdaptive Multi-Rate (AMR) speech codecMandatory speech CODEC speech processing functionsRelease 17TSVoice Activity Detector (VAD)

The quantized SNR SNR_q is used to determine the respective voice metric threshold vth, hangover count hcnt, and burst count threshold bth parameters:

(4.15)

where SNRQ is the index of the respective table elements. The VAD decision can then be made according to the following pseudocode:

if ( v(m) > vth + (m)) { /* if the voice metric > voice metric threshold*/
VAD(m) = ON
b(m) = b(m-1) + 1 /* increment burst counter */
if ( b(m) > bth ) { /* compare counter with threshold */
h(m) = hcnt /* set hangover */
}
} else {
b(m) = 0 /* clear burst counter */
h(m) = h(m-1) -1 /* decrement hangover /
if ( h(m) <= 0 ) { /* check for expired hangover /
VAD(m) = OFF
h(m) = 0
} else {
VAD(m) = ON /* hangover not yet expired */
}
}

Note that two 10 ms subframes are required to determine one VAD decision. The final decision is determined by the maximum of two subframe decisions, i.e.

if(VAD(m) == ON OR VAD(m-1) == ON) {
VAD_flag = TRUE
} else {
VAD_flag = FALSE
}