TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
Once the output level is once more below the Attack Threshold, the AGC enters the Hold Phase. In this phase, the
output level remains at, or below, the Attack Threshold. On entering the Hold phase, the AGC sets an internal Hold
timer, which then starts to decrement.
Before, the Hold timer can expire, the input signal level increases again, resulting in a second attack phase. After the
output level goes below the Attack Threshold again, the AGC re-starts the Hold phase.
Next, the input signal level is suddenly reduced. Since the AGC is still in the Hold phase, no change in the AGC
gain occurs, and the AGC output follows the reduction in input signal level.
When the Hold timer expires, the AGC enters the Decay phase again, and the AGC gain starts to increase.
The rate at which the gain increases during the Decay phase (decay time constant) and the rate in which the gain
reduces during the Attack phase (attack time constant) are programmable. Best results for speech recording are
normally achieved by selecting a fast Attack time constant (allows rapid gain reduction) and a slow Decay time
constant (allows only slow gain increase). This configuration causes the AGC to primarily respond to the peak
speech level, thus providing relative attenuation of any background noise audible during gaps in the speech. If the
Hold time is set to 2-3 seconds, the background noise will remain attenuated even during short pauses in the input
speech.
The AGC is automatically reset to the Start Gain value every time a new record session is started (that is, every time
a Record C1 command is issued).
9.10.3.1
Programming the AGC
Setting AGC parameters ( CF9xH):
Command C1:
1100 1111 1001 0
SELECTOR
(2-0)
(15-3)
Status S1:
1100 1111 1001 0
(15-3)
SELECTOR
(2-0)
Command C2:
Status S2:
Parameter Value
(15-0)
Parameter Value
(15-0)
90
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SANTA CLARA, CA 95054 PH: 408 986 – 4300 FAX: 408 986 – 4490
All specifications are subject to change without prior notice.
ETC [ ETC ]
