CT8022 Datasheet, PDF (91/194 Pages) List of Unclassifed Manufacturers – VOIP/VON G.723.1, G279AB TRUESPEECH CO-PROCESSOR

Version: 1.18
PRELIMINARY/CONFIDENTIAL
TrueSpeech® Co-Processor
Where SELECTOR is defined:
SELECTOR
000
001
010
011
100
101
110
111
Parameter Description
AGC Min Gain. The 16-bit parameter value used to set the AGC Min Gain is treated as a Q8
value. That is, the decimal point used to construct the value is considered to be to the right of
bit-8. So in Q8 notation, the value 1.00 is represented by the hex number 0100H (decimal 256).
The default value for this parameter is 0020H, this represents the fraction 0.125 in Q8 format.
The default min gain is a multiplier factor of 0.125, or one-eighth, or approximately -18 dB. The
min gain value can also be regarded as the maximum attenuation of the AGC. In this case, the
maximum attenuation is by a factor of 8 or approximately +18 dB.
AGC Max Gain. The 16-bit parameter value used to set the AGC Min Gain is treated as a Q8
value (see Min Gain). The default value for this parameter is 1000H. This represents the
fraction 16.0 in Q8 format. The default max gain is a multiplier factor of 16, or approximately 24
dB.
The default max and min gains give the AGC gain a range from -18 dB to +24 dB, which is a
range of 42 dB.
AGC Start Gain. The 16-bit parameter value used to set the AGC Start Gain is treated as a Q8
value (see Min Gain). The default value for this parameter is 0800H. This represents the
fraction 8.0 in Q8 format. The default max gain is a multiplier factor of 8 or approximately +18
dB.
Since the default decay time constant is much larger than the default attack time constant, the
default start gain is set high. This is because the time taken to reduce the gain (attack) is much
less than the time taken to increase the gain (decay). For example, if the initial speech level is
very high, the gain will be reduced quickly (attack) to adjust to the high input level. If the initial
speech level is low, since the decay time constant is large (slow), increasing the gain to amplify
the low speech level may take several seconds. Therefore, starting with a high gain that can be
quickly reduced provides the best initial performance.
AGC Hold Time. The 16-bit parameter value used to set the AGC Hold time has units of 250
microseconds. The default value of this parameter is 1F40H (8000 decimal) which corresponds
to a Hold Time of 2.00 seconds.
AGC Attack Time Constant. See Time Constant table. The default value of this parameter is
0005H.
AGC Decay Time Constant. See Time Constant table. The default value of this parameter is
000DH (14 decimal).
AGC Attack Threshold. The AGC Attack Threshold is the AGC output value above which the
AGC enters the Attack phase (gain reduction). The default value of this parameter is 2000H.
The value can be set anywhere in the range of 0000H to 7FFFH. Note that 7FFFH is the
maximum internal (digital) signal level. Therefore, a value of 2000H selects AGC attack when
the peak signal amplitude is above 0.25 full scale.
AGC On/Off. Setting this parameter to 0001H enables AGC operation, setting the parameter to
0000H disables AGC operation. By default, the parameter is 0000H with the AGC in the Off
state.
Reading AGC parameters ( CF8xH ):
The AGC parameters programmed can be read back using the command below:
Command:
1100 1111 1000 0
(15-3)
SELECTOR
(2-0)
Status:
Parameter Value
(15-0)
CT8022A11AQC FW Revision 0118
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91
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All specifications are subject to change without prior notice.