CT8022 Datasheet, PDF (92/194 Pages) List of Unclassifed Manufacturers – VOIP/VON G.723.1, G279AB TRUESPEECH CO-PROCESSOR

TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
Table 9-1: Time Constant Table
Time Constant Parameter
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
attack/decay fraction per 125
microseconds = 1/2^(n+1)
U(n+1) = U(n) - U(n) * fraction
0.5
0.25
0.125
0.0625
0.03125
0.015625
0.0078125
0.00390625
0.001953125
0.0009765625
0.00048828125
0.000244140625
0.0001220703125
0.00006103515625
0.00003051757813
0.00001525878906
Time Constant inms
(assuming 8 KHz sample rate)
250 us
512 us
1ms
2ms
4ms
8ms
16ms
32ms
64ms
128ms
256ms
512ms
1024ms
2048ms
4096ms
8192ms
In the Attack phase (gain decreases) , the AGC gain is recalculated every CODEC sample (125 us) such that:
AGC gain = AGC gain - ( ( AGC gain - min AGC gain) * 1/2^(n+1) )
This behaves as an approximately exponential decay from the current instantaneous gain value towards the min AGC
value.
In the Decay phase (gain increases), the AGC gain is recalculated every CODEC sample (125 us) such that:
AGC gain = AGC gain + ( (max AGC gain - AGC gain) * 1/2^(n+1) )
This behaves as an approximately exponential decay from the current instantaneous gain value towards the max
AGC value.
Note that the time constant, is the time that it takes for an initial value to decay to 1/e of its initial value where:
e = 2.71828.
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DSP GROUP, INC., 3120 SCOTT BOULEVARD
CT8022A11AQC FW Revision 0118
SANTA CLARA, CA 95054 PH: 408 986 – 4300 FAX: 408 986 – 4490
All specifications are subject to change without prior notice.