EAW DX1208, Help File, Page: 27 / 64

Target level, the gain is reduced; when it falls below the Target level it is
increased, so that the output volume is always being driven towards the
Target .
•
Threshold When the input volume exceeds the Threshold , the AGC is activated
and makes dynamic volume adjustments that drive the output volume
level towards the
Target level. When the input volume drops below the
Threshold, the AGC stops adjusting the gain and holds it at the last set
value. The AGC is most effective when it makes volume adjustments
only when a valid program source is present, but not when the source is
absent. DX Navigator limits the
Threshold values to be
≤
the Target .
For example, in a boardroom environment where multiple individuals
each have their own microphone, every microphone will pick up the
sound not only of the assigned speaker, but also background noise and
the sound of every other speaker in the room. To be effective, the AGC
should act only on the speaker’s voice, but not act on the background
noise. Therefore set the
Threshold just below the minimum volume
level of the source to prevent the AGC from acting on background
noise. This prevents the AGC from making unwanted gain increases in
the presence of background noise which will cause the source to be
louder than desired when the source resumes. For sources which
slowly fade to silence (as may happen with subscription music feeds
and CD music sources), set the
Threshold approximately [10] to [15 dB]
below the Target .
•
Attack Attack controls the rate of volume change (both increase and decrease)
when the source volume exceeds the Threshold . Attack settings will
vary depending on the nature of the source, but generally should be set
slower than the rates typically used with compression.
With slow
Attack times, very little AGC gain change will occur between
when a gap/pause in the source occurs and when the source resumes.
However, the AGC will not react as quickly to rapid increases or
decreases in the program volume. With faster
Attack times the AGC
will react more quickly to sudden changes in program volume, but
greater gain changes will occur between silence gaps and the
resumption of the source, potentially causing ‘pumping’ effects
associated with compressors. Set the
Attack so that the volume change
rate change sounds natural to the ear and does not draw attention to
itself.
•
Ratio The AGC Ratio control determines the ratio at which the output volume
increases with respect to the input volume, and in that respect is
identical to the Compressor
Ratio control. The higher the Ratio , the
less the output volume changes with for any given variance in input
volume. However, the input/output transfer curves of each differ with
respect to how they intersect with the
Threshold and Target values. In
the Compressor, the non-unity portion of the transfer curve passes
through the
Threshold ; in the AGC, the non-unity portion passes
through the Target . The difference is illustrated by the graph below.
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