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FALCON · User Manual · ENG
PROCESS
5.4.1
AUTOMATIC GAIN CONTROL – AGC
The audio volume could very annoying in the tune across the broadcast band in stations were it not for automatic
gain control (AGC).
The AGC filter attempts to make the audio level constant, without causing noticeable changes in the sound. If sudden
spikes are present, it can remove those spikes without lowering the output level too much, to avoid pumping and
similar annoying effects. The AGC never increases the incoming audio level, it only decreases it if it gets too loud.
Three different zones are defined for the AGC which are called attack zone, release zone and dead zone, shown in
next figure.
Drive: The AGC Drive adjusts the signal level to the slow dual-band
AGC and this determines the amount of reduced gain in the AGC.
Attack: one of these parameters which control the behavior
(function) of the AGC. The attack time is the time that we control
between two attack events. The AGC’s attack zone is set to be
above 0.8 (relative to the supply voltage) and below -0.8. If the
output of the VGA (Variable Gain Amplifier) is within the attack
zone the gain is reduced by one gain step for an attack time
Release: the release time is the time that we control between two
release events. The AGC’s release zone is set to be between 0.6 to
-0.6 and the zone between the attack and release zones is called
dead zone which basically no attack or release happens in this
zone.
Gate Threshold: control the limit of the lowest input level will recognize as a program. lower levels are considered
as noise or background sounds and rise the AGC to the gate, effectively freezing gain to prevent noise breathing.