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The
recovery
time
of
the
compression
function
is
adjustable
in
the " Master"
band
only by means of the RELEASE TIME control. In addition, a gating circuit
slows the recovery time of the compression function if the input program level
drops
below
a threshold
adjustable
by
the
GATE
THRESHOLD
control,
thus
preventing " noise swish- up" during pauses or during low-level material. In GATED
mode,
recovery
occurs
toward - 10dB
gain
instead
of
OdB,
thus
avoiding
noise
pump- up on very noisy material like 16mm optical sound tracks.
The " Bass"
timing
circuitry
is
similar
to
the " Master"
timing
circuitry,
and
performs
all
of
the same
functions. Its time constants are
optimized for most
natural, dynamic sound.
Both
timing
circuits
process
the
signal
in
logarithmic
form,
and
have
low-
impedance outputs. The timing circuits drive exponential converters which provide
control- current outputs for the " Master" and " Bass" VCA's. The BASS COUPLING
control provides the ability to sum a controlled amount of the " Master" timing
circuit
output
into
the " Bass"
exponential
converter,
where
it
sums
with
the
output of the " Bass" timing circuit in a dB- linear manner.
Extensive
gain reduction metering is provided.
Since
the outputs of
the timing
circuits
are
dB- linear,
the
gain
reduction
meters
are
provided
with
dB- linear
scales.
The
output
of the " Master" timing module is applied to a peak detector which
"holds"
the
fast- limiting
component
of
the
control
voltage
until
the
gain
reduction meter ballistics have a chance to " catch up". The output of this peak
detector
drives
the " Master" gain reduction meter, which shows the true
peak
value of the gain reduction.
The
output
of
the " Master"
timing
module
also
drives
a slewrate-limited
amplifier
which
removes
the
fast
limiting
spikes
from
the
voltage,
and
which
drives the " compressor" meter to show the amount of slow compression occurring.
By
subtracting
the
output
of
the
slewrate-limited
amplifier
from
the
peak
detector,
the
fast
peaks
only
are
derived.
This
difference
signal
feeds
the
"Limiting" meter.
The
output
of
the " Bass"
timing
circuitry
contains
a much
smaller
fast
peak
limiting
component
than
does
the
output
of
the " Master"
timing
circuitry.
No
peak
detection is necessary to assure accurate metering, and the output
of the
"Bass" timing circuitry thus drives its gain reduction meter directly.
Except
for the " Limiting" meter, all G/R meters are calibrated from - 15dB to
+10dB gain reduction. " 0" thus corresponds to the normal gain of the system in
its quiescent, gated state. In this state, the VCA gains are in fact
10dB below
maximum.
The LIMITING meter is calibrated from 0 to 5dB for best resolution. When the
RELEASE TIME control is operated in the slow part of its range, the LIMITING
meter will ordinarily show little activity. However, as the release time is speeded
up, the LIMITING meter will become more active, typically reading full-scale on
transient material.
A-5
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