4.3.5 Frame SNR and Long-Term Peak SNR Calculation

06.943GPPTSVoice Activity Detector (VAD) for Adaptive Multi Rate (AMR) speech traffic channels

The instantaneous frame SNR, SNR, and long-term peak SNR, SNRp(m), are used to calibrate the responsiveness of the VAD decision. When the frame count is less than or equal to four (m  4) or the forced update flag (sec 4.3.10) is set (fupdate_flag == TRUE), then the SNR’s are initialized as:

. (4.9)

Otherwise, the instantaneous frame SNR is generated by:

(4.10)

and the long-term peak SNR is derived by the following expression:

. (4.11)

The long-term peak SNR is then quantized in 3 dB steps and limited to be between 0 and 19, as follows:

(4.12)

where is the largest integer  x (floor function).