A.1 Simplified block filtering operation

06.323GPPTSVoice Activity Detection (VAD)

Consider an 8th order transversal filter with filter coefficients a0..a8, through which a signal is being passed, the output of the filter being:


If we apply block filtering over 20 ms segments, then this equation becomes:


If the energy of the filtered signal is then obtained for every 20 ms segment, the equation for this is:


We know that (see GSM 06.10, clause 3.1.4):


If equation (3) is expanded and acf0..acf8 are substituted for sn then we arrive at the equations: