TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
9.10.3
Automatic Gain/Level Control (AGC or ALC)
The CT8022 includes an AGC feature that can be used in record mode for automatic level adjustment when
recording messages.
Note: For optimal Acoustic Echo Canceller (AEC) performance, the Host should ensure that the AGC is
switched Off before activating the AEC.
The purpose of the Acoustic Echo Canceller (AEC) is to attenuate, as far as possible, acoustic echoes from the
speaker that are picked up by the microphone. The purpose of the Automatic Gain Control (AGC) is to amplify
low-level signals that the microphone picks up. Consequently, the AGC and AEC tend to conflict with each other.
The CT8022 incorporates an additional feature that reduces the amount of conflict between the AEC and AGC. The
AGC includes a feature that reduces that rate of gain increase allowed when the AEC status indicates that the active
speech direction is from the remote talker. If the user requires that the AGC and AEC operate concurrently, then the
following recommendations should be followed:
1. Limit the maximum AGC gain to the lowest value that produces acceptable results.
2. Make use of the hold time feature of the AGC to minimize gain increases during short pauses in conversation.
3. Increase the amount of Echo Suppression (loop attenuation) used by the echo canceller to compensate for the
additional gain introduced by the AGC.
4. Activate the advanced AEC features.
Activating the AGC disables the Record Volume Control. The Record Volume Control has no effect when the AGC
is active. However, Record Volume Control setting changes are retained by the CT8022 and will become effective
when the AGC is de-activated.
The AGC provides the following parameters, which are Host-programmable:
The maximum gain (max amplification) provided by the AGC
The minimum gain (max attenuation) provided by the AGC
Max Gain:
Min Gain:
The AGC output signal level above which attack occurs in the attack phase (gain
reduction) and below which decay occurs when in the decay phase (gain increase).
Attack Threshold:
This controls the rate at which the gain decreases during the attack phase
This controls the rate at which the gain increases during the decay phase.
Attack time-constant:
Decay time-constant:
Hold Time:
The length of time that the AGC gain is held constant following the end of the attack
phase and before the beginning of the decay phase.
The initial gain setting to use when the AGC is activated. This may be set anywhere
between the min and max gain values.
Start Gain:
88
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.
ETC [ ETC ]
