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Detailed Parameters
Section 6
6.12 - Automatic Gain Control (AGC) Insert
The Automatic Gain Control Insert is available in the DriveRack 4800 and 4820 in both the Input and
Output Insert modules. Automatic Gain Control (or AGC) is used to keep the average level of a signal
constant. This is done by selecting a desired Target output level and the Window around that Target. The
AGC keeps the signal within the Window around the selected Target by slowly adjusting the gain. The
maximum gain that can be applied to the signal is selected by the Gain parameter. When the input signal
falls below the Threshold parameter, the AGC stops adding gain and returns to unity. This prevents the
AGC from adding gain when there is no signal present and raising the system noise floor. Within the AGC,
high level peak signals are reduced by a fast acting Limiter to prevent clipping and distortion. The AGC
Threshold meters show what region of the AGC the input signal is in. The T (yellow) indicates the signal
is within the Window. A red + indicates the signal is above the target window, and a green - indicates the
AGC is adding Gain and is at or below the window. When the Threshold meter is turned off, the signal
is below the Threshold. The Limiter also has a Threshold meter indicating when the signal has crossed the
Limiter Threshold.
AGC On/Off switch
This turns the AGC module On and Off.
Threshold fader
The Threshold sets a lower limit to the AGC. It prevents the AGC from adding gain below the Threshold
and raising the noise floor. The Threshold range is between -80 to -50dBFS.
Gain fader
This adjusts the maximum amount of Gain that can be added by the AGC, and ranges between 1 and
20dB.
Target fader
The Target parameter defines what you would like the average output level of the AGC to be. If the average
level of the signal rises above the Target the gain will be reduced. If the average level of the signal is below
the target Gain will be added. The Target range is between -40 and -1 dBFS.
DriveRack
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4800/4820 User Manual
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