The
Exponential mode is useful
when
the 424A is used
to ride gain on wide
dynamic-range program material (such
as
certain vocalists),
yet
a
very "open"
sound (associated
with
slow
release times)
is
desired.
The GATE
THRESHold control determines
the input level at which the
compressor
release
process
becomes
"gated".
When
this happens, the compressor
gain "freezes"
wherever it
happens to be, then immediately starts slowly
drifting
to a
point
pre-determined by
the setting
of
the IDLE GAIN control
(see below).
The
fast limiting release
process is
unaffected.
Under
this
condition, the
GATED lamp is lit.
The
gating
function can
be used
to prevent noise "pump-up" or
"breathing"
during
pauses and/or to control hiss from
empty tracks at the
beginning
of
a
mix.
A conventional non-gated compressor would recover to full gain,
increasing
noise levels.
This
function is not the same
as
the familiar
"noise gate" or
"expansion"
function. If further noise reduction is desired, a conventional full-featured noise
gate can be used ahead of the 424A. However, if the
424A's
IDLE GAIN
control is set to match the average amount of gain reduction, more subtle
processing
than
that produced by a noise gate is achieved since
noise will
neither increase nor
decrease
during pauses.
The gating function is defeatable by turning
the
GATE THRESHold
control
fully
counterclockwise. In
a
sense,
the gating
function
is
the opposite
of
the
Exponential release function, in that
the
gating function slows and redirects
the release characteristic during pauses, while the Exponential function
speeds
up the release process. However, the gating
function
can
still be
operated when
in the EXPonential
release
time
mode, and it is possible that the two
functions
may
complement
each other in certain
applications. Only experimentation can
tell!
The VCA
LEVEL meter
indicates the peak output level of the 424A
compressor/limiter voltage-controlled
amplifier (VCA). Ordinarily,
if will
unambiguously
indicate
VCA
clipping, which occurs
at approximately "+3dB"
on
the meter.
The
meter
accurately captures and holds
the peak level
of
even the fastest
program peaks,
and
will
read
within
0.5dB of
fhe frue peak value of a 10
microsecond
pulse.
However, it is possible
that
VCA clipping
will
not
be
identified if high-energy,
high-frequency
program material
is processed by both the compressor/limiter
and
de-esser sections
simultaneously. In this
case,
clipping may occur in the
compressor/limiter
section of the VCA,
yet
the
de-esser
section of the VCA
may reduce the final
VCA output
level
as observed on the VCA
LEVEL meter
such
that
clipping is not indicated.
(Ordinarily, a moderate amount
of clipping
of program material of
this
type
is not audibly offensive.)
The OUTPUT TRIM control
is
a gain control used
to control or to
prevent
clipping
in
the VCA. IT
IS NOT
A
CONVENTIONAL
OUTPUT
ATTENUATOR
CONTROL, AND
MUST NOT BE USED
AS SUCH,
LEST THE VCA BE
OPERATED IN
A NON-OPTIMUM PART OF
ITS GAIN
CONTROL RANGE!
13
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