Digital Signal Processing Reference
In-Depth Information
Background
Noise
Adaptation
Input
signal
Filter
Bank
Threshold
Adaptation
VAD
Decision
Band Energy
Computation
Band SNR
Sum
Active/
Inactive
Hangover
Figure 10.5
Block diagram of ETSI AMR VAD option 1
Tone flag
Pitch flag
Noise
Update
Decision
Spectral
Deviation
Estimate
Input
signal
Background
Noise
Adaptation
FFT
Band Energy
Computation
Band SNR
Estimate
VAD
Decision
Active/
Inactive
Peak-to-
Average
SNR Ratio
Figure 10.6
Block diagram of ETSI AMR VAD option 2
Furthermore, noise adaptation may not be accurately performed by measur-
ing the spectral deviation when subband energies fluctuate rapidly. Thus,
AMR2 changes the VAD threshold in an adaptive way together with the vari-
ation of burst and hangover counts. The hangover control is performed by
measuring the peak-to-average SNR, in which the average SNR is calculated
using AR-adaptation with the increased instantaneous SNR. In other words,
for an increase of the peak-to-average SNR, it decreases the hangover andburst
counts while increasing the VAD threshold. The block diagram of AMR2 is
shown in Figure 10.6.
10.2.4 TIA/EIAIS-127/733VAD
CDMA-based digital cellular systems have a natural structure for incorporat-
ingVAD, calleda ratedeterminationalgorithm(RDA),whichgives substantial
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