User Manual

ALF-DSP 88-U
-18-
Output Gain: Also called gain compensation. If the compressor significantly reduces the level of the signal, it may
need to enhance the output gain to maintain the volume. Output gain applies to all parts of the signal and is
unrelated to other parameter settings of the compressor.
Gain Reduction (G.R.) and output Level Meter: G.R. indicates the compressor's compression amount; output refers
to the output level of the signal that has passed through the compressor module (post compression). The
compression amount is displayed in an inverse level meter. If the input signal and threshold are set as -6dB and -
30dB, respectively, and the ratio is 2:1, then the compression amount is 12dB; the G.R. level meter indicates around
-12dB and output indicates around -18dB.
Limiter
The limiter only has one key task: make sure that the signal will not exceed the threshold level in any way. By
adjusting the compressor's control parameters, its working modes will be very similar to those of the limiter. The
core working principle of a limiter is that it focuses on the signal below the threshold level as well as how the gain
attenuation is produced before the occurrence of overshoot signal. The limit period consists of two processing
stages: during the first stage, there is a minor limit, but the overshoot signal will not be processed; during the
second stage, if there is overshoot signal, it will attenuate with a very high ratio.
The limiter only provides two parameters: Threshold and Release Time. In terms of signal processing, occasional
clipping will be solved with a limiter, while the signal level will be attenuated in terms of frequent clipping.
3.4.4 Automatic Gain Control
Automatic gain control (AGC) is a type of compressor. Its threshold is set at a very low level with middle-to-slow
attack time, long release time , and low ratio. The purpose is to improve the signal with an uncertain level to a target
level, while maintaining the dynamic range at the same time. Most of the auto gain control includes silent detection
to prevent the gain attenuation loss during the silent period. This is the only function that distinguishes auto gain
control from an ordinary compressor / limiter.
Auto gain control may be adopted to normalize the level of CD players that play background music, foreground
music and music on hold, as to eliminate the changes in the level of some paging microphones.