06.943GPPTSVoice Activity Detector (VAD) for Adaptive Multi Rate (AMR) speech traffic channels
If (and only if) the update flag is set (update_flag == TRUE), then update the channel noise estimate for the next subframe by:
where Emin is the minimum allowable channel energy, and n is the channel noise smoothing factor. The channel noise estimate shall be initialized for each of the first four frames to the estimated channel energy, i.e.:
where Einit is the minimum allowable channel noise initialization energy.