Grass Valley AMX-3981 2014 - Manual (Page 90)

GUIDE TO INSTALLATION AND OPERATION
84 | AMX-3981
For reference, the crossover frequencies are:
• Band 1 (Low Bass): 20 Hz - 60 Hz
• Band 2 (Mid Bass): 30 Hz - 200 Hz
• Band 3 (Low Mid): 170 Hz - 1.15 kHz
• Band 4 (High Mid): 950 Hz - 6.1 kHz
• Band 5 (Brilliance): 5.2 kHz - 24 kHz
Input AGC
The input AGC is a very slow acting front-end gain control with a 36dB
gain range whose only purpose is to make sure that the following
processing stages are fed with the correct average audio levels. It is
basically the automatic equivalent of an operator slowly riding a gain
control on a console to keep the audio close to reference level.
Wideband in nature, the AGC is not meant to perform rapid gain
reduction or expansion as its actions will be more audible, as with all
wideband gain processors. As a slow gain rider, its actions are nearly
inaudible thanks to the multiband processing that follows it. The AGC
has two stages of gating where the gain expansion is slowed or stopped
to prevent background noise increasing.
Adjustable parameters are:
• Gate Threshold: 0dBFS to -90dBFS (default: -30dBFS). Gating
sets the point at which the AGC release is made extremely slow
to prevent increasing background noise and allow the AGC to
return to unity gain.
• Freeze Threshold: 0dBFS to -90dBFS (default: -42dBFS). Freeze
stops all gain change (i.e. when the audio drops to silence), and
remains frozen at its current gain value until the threshold is
exceeded.
NOTE: Adjust Gate and Freeze to match plant practices. Very quiet
audio (such as a golf match) benefits from having processing frozen
when input audio drops below a given level to prevent “boosting the
cricket” sounds.
• Ratio: 1:1 to Inf:1 (default: 12.0:1)
• Range: 0dB - 36 dB (default: 24dB). Range sets how much gain expansion above unity is performed, and this
amount is subtracted from the total AGC gain range of 36dB, so the default value allows for 24dB of expansion
and 12dB of compression. This adjustment is reflected in real time by changing the AGC meter scale.
• Threshold: -18dBFS - 0dBFS (default: -16dBFS)
• Attack: 0 - 150, slowest - fastest (default: 21)
• Release: 0 - 150, slowest - fastest (default: 47)
• Progressive Release: 0 - 100, slowest - fastest (default: 50). Sets the speed at which the release time is
increased faster at very low gain values. This feature approximates a logarithmic release to help recovery from
dramatic gain reduction more quickly.
Figure 6.12 ALC - Input AGC