Datasheet

Decay Time
Target
Level
Input
Signal
Output
Signal
AGC
Gain
Attack
Time
TLV320AIC3107
SLOS545D –NOVEMBER 2008 –REVISED DECEMBER 2014 www.ti.com
Table 2. AGC Decay Time Restriction
NADC RATIO MAXIMUM DECAY TIME (seconds)
1.0 4.0
1.5 5.6
2.0 8.0
2.5 9.6
3.0 11.2
3.5 11.2
4.0 16.0
4.5 16.0
5.0 19.2
5.5 22.4
6.0 22.4
10.3.3.2.2.4 Noise Gate Threshold
Noise Gate Threshold determines the level below which if the input speech average value falls, AGC considers it
as a silence and hence brings down the gain to 0 dB in steps of 0.5 dB every FS and sets the noise threshold
flag. The gain stays at 0 dB unless the input speech signal average rises above the noise threshold setting. This
ensures that noise does not get gained up in the absence of speech. Noise threshold level in the AGC algorithm
is programmable from –30 dB to –90 dB relative to full scale. A disable noise gate feature is also available. This
operation includes programmable debounce and hysteresis functionality to avoid the AGC gain from cycling
between high gain and 0 dB when signals are near the noise threshold level. When the noise threshold flag is
set, the status of gain applied by the AGC and the saturation flag should be ignored.
10.3.3.2.2.5 Maximum PGA Gain Applicable
Maximum PGA Gain Applicable allows the user to restrict the maximum PGA gain that can be applied by the
AGC algorithm. This can be used for limiting PGA gain in situations where environmental noise is greater than
programmed noise threshold. It can be programmed from 0 dB to +59.5 dB in steps of 0.5 dB.
Figure 20. Typical Operation of the AGC Algorithm During Speech Recording
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