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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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