— 21 —
There will, of course, be a range over which the AGC wanders; it
is not realistic to expect the indicator to hover right at the
0dB
mark all the time. But the indicator should spend about as
much time above
0dB
as it does below.
The dB gain numbers shown below each input gain slider are
somewhat arbitrary, but have been scaled so that
0dB
equates
to the program
average
level at nominal studio line level fig-
ures. This might be +4dBu for analog inputs or –20dBFS for
digital feeds. For example, a well-tempered +4dBm program
line would suggest an
Analog Gain
setting of
–4.0dB
, and digital
program levels with a typical headroom allowance of 20dB (rel-
ative to 0dBFS) would need a
Digital Gain
figure of
0dB
. Again,
the scaling holds true more for actual program material than
for steady-state tones.
THE HIGH-PASS FILTER
The DAVID IV is equipped with a steep high-pass filter to lessen
the modulation-robbing effects of unwanted subaudible pro-
gram audio components. The term ‘unwanted’ is the keyword
here, as “mega-bass” seems a mandatory part of any car audio
installation, and a “big bottom-end” characterizes the sonic
signature or nearly all contemporary music stations.
Navigate to:
Processing / High Pass Filter
:
Once you have arrived at this menu
push
the jog wheel to enter
the adjustment mode. Then as you
turn
the jog wheel the
screen animation will illustrate filter action.
This filter is a 4
th
order (24dB/octave) high-pass, which may be
set for a turnover frequency (–0.15dB point in this case) be-
tween
20Hz
and
65Hz
. The factory default is
20Hz
, which is
probably a valid setting for any music format, unless you have
severe turntable rumble (say, what?), noisy studio air condition-
ing, do a lot of outdoor sports remotes in windy stadiums or
have creditors pounding on the front door.
This high-pass function has been included in the DAVID IV de-
sign to define a low-frequency limit to the station airchain. But
the use of this high-pass filter should generally be considered a
Band-Aid® fix for problems that are best addressed at their
source.
Summary of Contents for 719
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