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AGC – Enhanced AGC

Automatic gain control (AGC) allows a microphone’s signal to automatically adjust to compensate for variations in volume from different talkers, or variations due to a single talker moving relative to the mic. The ControlSpace® Enhanced AGC provides a simple, flexible way to provide up to 30 dB of boost or cut, and can process multiple, interactive channels simultaneously.

The three primary controls on the Enhanced AGC are Activity Threshold, Target Minimum, and Target Maximum.

It is important to prevent an AGC from reacting to low level signals such as background noise. The Activity Threshold control sets the minimum level required before the Enhanced AGC will affect the channel gain. This control should be set just above the maximum anticipated background noise. Setting this level too low will cause the Enhanced AGC to always boost the channel gain, rather than only when the mic is being used.

Enhanced AGC

Target Minimum and Maximum

Many AGCs have a target value and the AGC boosts or cuts the signal to push the input signal to the target. This results in a signal that is always being modified. The ControlSpace Enhanced AGC uses a Target Minimum and a Target Maximum.

  • If the signal is below the Target Minimum, the Enhanced AGC increases the channel gain to move the signal towards the Target Minimum.
  • If the signal is above the Target Maximum, the Enhanced AGC reduces the channel gain to move the signal down towards the Target Maximum.
  • If the signal is between the Target Minimum and Maximum, the channel gain is left at unity and there is no modification of the signal. This results in more natural sounding speech when the signal is within the acceptable range.

Rate, Range, and Hold

The Enhanced AGC provides independent control over the rate, range, and hold for the boost and cut functions. This allows the response of the Enhanced AGC to be tailored to the specific needs of each situation.

The boost and cut “Rate” settings control the speed of changes made by the AGC. Slower changes will sound smoother and more natural while faster changes provide better protection against excessive volume. The boost and cut rate settings are completely independent of each other. Depending on the use environment, a slower boost rate such as 3 dB or 6 dB per second will provide a very natural sounding gain adjustment. A much faster cut rate such as 24 dB per second is often desired to quickly react to excessively loud signals.

The boost and cut “Range” settings control the amount of boost and cut provided by the Enhanced AGC, up to a maximum of 30 dB. Independent controls allow the Enhanced AGC to provide large amounts of gain reduction for excessively loud signals while only providing smaller amounts of gain boost for quieter signals.

The boost and cut “Hold” settings determine how long the Enhanced AGC will maintain the current boost/cut to the channel gain when the signal drops below the Activity Threshold. When a talker momentarily pauses while speaking, it is likely that they will resume speaking at the same level. The Hold setting allows the AGC to pause while the talker pauses so there is less likely to be a need for an immediate change when the talker begins speaking again. If the signal remains below the Activity Threshold longer than the Hold time, the Enhanced AGC will begin moving the gain back to unity.

If the signal has dropped below the Activity Threshold and the Hold time has not run out yet, the Hold indicator at the top of the channel will illuminate to indicate that the Enhanced AGC is holding the current boost or cut to the channel gain.

Enhanced AGC - Rate, Range, and Hold Figure

Channel Meters

The Input meter at the top of each channel shows the level of the Enhanced AGC input signal. This is the level of each channel’s signal prior to being modified by the Enhanced AGC and does not reflect the gain changes made by the Enhanced AGC.

The Gain meter at the top of each channel shows how much gain is currently being applied to each channel by the Enhanced AGC. In addition to providing a visual representation of how the Enhanced AGC is modifying the channel signal, this meter shows how much gain is being applied during the Hold state when the input signal is below the Activity Threshold.

Enhanced AGC - Channel Meters Figure

Master Controls

The Total Gain meter in the Master section of the Enhanced AGC control panel shows the combined total amount of system gain being applied by all channels of the Enhanced AGC block. This includes both boosts and cuts being applied to any channel.

The Maximum Total Gain control allows you to limit the total amount of gain being applied by all channels combined. While it may be safe to allow any single channel to have 9 dB of boost added to it, having 9 dB of boost applied simultaneously to each of the 16 channels may result in feedback or excessive noise. If the amount of gain to be applied to all channels would result in a total greater than the Maximum Total Gain, the gain being applied to each channel is reduced. For example, if the Maximum Total Gain were set to 12 dB, and two channels each needed to receive 6 dB of boost, they would each receive their full boost. If four channels each needed to receive 6 dB of boost, that would exceed the Maximum Total Gain, so each channel would only receive 3 dB of boost. If one of those channels were to drop out and return to unity gain, each of the remaining three channels would receive 4 dB of boost.

Enhanced AGC - Master Controls Figure