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SELECTING THE INPUT
Inputs
The DAVID IV has both an AES3 (stereo) digital input and indi-
vidual left/right analog inputs. Either set can serve as the pro-
gram input to the unit, and the selected input is shown on the
Now Playing
Webpage. Characteristics of these inputs are dis-
cussed in the Specifications pages and in Section II of this
manual.
Inputs are selected and level-adjusted on the
Setup
Webpage
and under the corresponding
Setup / Audio Input
front-panel
menu.
SETTING INPUT GAIN
Importance of
AGC Action
The DAVID IV has an intelligent dual-slope ‘windowed’ AGC
(Automatic Gain Control), a long-term ‘gain-riding’ utility to
normalize input levels between sources and individual songs.
AGC capture range is ±18dB, meaning that the input signal can
wander aimlessly over this 36dB range and be automatically
corrected to the proper level for subsequent processing stages.
AGC gain is shown in the bargraphs that headline each
Pro-
cessing
Webpage and by the front-panel LED bargraph display.
AGC has been designed for symmetrical correction around a
resting-point of
0dB
, or unity gain. It will bring up lower levels
and pull down higher ones at the selected correction rate. AGC
action is ‘gated’ to freeze the gain during brief program pauses,
returning it to the
0dB
resting point during extended periods of
silence. The
Now Playing
Webpage and front-panel gate indica-
tors glow when the gate is ‘open,’ AGC active, and dark with no
valid input signal.
AGC is considered a processing parameter of the DAVID IV, but
one that, by design, does not really make a contribution to the
station’s “signature sound.” The sole purpose of the AGC is to
normalize levels ahead of the other processing stages without
adding coloration. This is possible only with a wideband AGC,
which should always be the first stage in any comprehensive
audio processing system. “Multiband AGC” is a misnomer.
Long-term
leveling
in individual frequency ranges may have
utility in some instances, but this still amounts to spectrum-
shaping, a subjective parameter. Using multiband AGC to nor-
malize levels from diverse sources or to correct for sloppy op-
erators is analogous to turning the listening volume in your liv-
ing room up and down using the individual sliders of a graphic
equalizer.
DAVID IV AGC gain is based on both the peak and average en-
ergy content of the program signal. Regardless of changes you
might want to make in AGC operation for a specific need (this
will be addressed later), check that the AGC is set to factory de-
faults during setup of input levels. Check under
Processor
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