— 18 —
Turn
the jog wheel to position the brackets around either the
Digital
or the
Analog
audio input, and then
press
the jog
wheel to confirm and save the selection.
SETTING INPUT GAIN
Importance of
AGC Action
The DAVID IV has an intelligent AGC (Automatic Gain Control)
that effectively ‘rides gain’ on the input signal. The AGC has a
capture range of ±18dB, meaning that the input signal can
wander aimlessly over this range and be automatically correct-
ed to the proper level. AGC gain is shown by a front-panel LED
bargraph.
AGC has been designed for symmetrical correction around a
resting-point of
0dB
(unity) gain. It will bring up lower levels
and pull down higher ones at the chosen correction rate. AGC
is ‘gated’ to freeze the gain when the program pauses and slow-
ly return it to the
0dB
resting-point during extended periods of
silence. The front-panel
GATE
indicator glows when the gate is
‘open’; that is, when the AGC is active.
AGC is considered a processing parameter of the DAVID IV, but
one that, by design, does not make an audible contribution to
the station’s “signature sound.” The sole purpose of the AGC is
to normalize levels ahead of the other processing stages with-
out adding coloration. This is possible only with a wideband
AGC, which should always be the first stage in any comprehen-
sive audio processing system. “Multiband AGC” is a misnomer.
Long-term
leveling
in individual frequency ranges may have
utility in some instances, but using this to normalize levels
from diverse sources or to correct for sloppy operators is anal-
ogous to turning the listening volume in your living room up
and down using the individual sliders of a graphic equalizer.
The AGC delivers a signal of uniform level to subsequent pro-
cessing stages, and AGC gain is based on both the peak and av-
erage energy values of the program content. Regardless of
changes you might want to make in AGC operation for a specif-
ic need (this will be addressed later), check that the AGC is set
to factory defaults during setup of input levels. Navigate to:
Processing / AGC
to confirm that the AGC is
Active
with a
Cor-
rection Rate
of
5
and
Max Gain
of
18.0dB
as shown here:
Using Test
Tones
Although a “zero-VU” test tone may certainly be used in setup,
input gain is most accurately set with actual program material.
Here’s why.
Summary of Contents for David IV
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