dbx 161 Manuel d'instruction - Page 7
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A REVIEW
Compressor
A
variable gain amplifier
whose
gain decreases
as
its
input
level
increases past the
threshold
point.
Limiter
A
compressor
with
a high
compression
ratio;
the high
ratio
maintains
essentially
constant
output
level
despite
any
increase
in
input
level
above
the threshold.
Compression
Ratio
The
ratio,
in
dB,
of
input
level
change above
threshold,
to
output
level
change.
A
compressor
whose
output
level
changes
IdB
for
a
2dB
input
level
change
has a 2:1
Compression
Ratio.
Threshold
The
level
at
which compression
begins,
dbx
Model 160
and Model
161 compressor/limiters
have
adjustable
thres-
holds.
When
the input
level
is
below
the
set
threshold,
and
the
Output Gain
control
is
set at
"OdB"
(12
o'clock), the
unit functions
as
a 1:1 amplifier
(a
unity gain
device).
When
the input
level
is
above
the
set
threshold, the unit
functions
as
a
compressor,
or
as a
limiter,
depending
on
the
com-
pression
ratio selected.
a=Unaltered
Signal
Envelope
Fig.
4
-
Attack
&
Release
Times
"track" the envelope
of
the input
signal.
Fig.
5
-
Input
and Output
Levels
at
various
compression
ratios.
SPECI
FICATIONS—
160
INPUT
Type
Actual
Impedance
Connector
Maximum
Level
Balanced
(differential)
transformerless.
50K-ohms
(25K-ohms
when
used
in
unbalanced
mode, one
side
tied
to
ground).
Jones-type
barrier
strip.
+21dB
(8.7V)
OUTPUT
Type
Actual
Impedance
Connector
Max.
Level Bridging
(lOK-ohm
or greater
Z)
Matching
(600-ohms)
Output
Level
Adjust
(Continuous)
Protection
Single-ended,
ground-compensated;
suitable for driving
balanced
or
unbalanced
loads.
25
ohms
(typical);
will
drive
low
or
high
impedance
loads.
Jones-type
barrier
strip.
+26dB
(15.5V)
+24dBm
(12.3V)
±20dB
from
unity gain point.
FET
circuits
prevent
power
turn-on or
turn-off transients
from
reaching the output.
DISTORTION*
0.075% 2nd
harmonic
at
infinite
compression
at
+4dBm
output
0.5%
3rd
harmonic
typical
at
infinite
compression
ratio
EQUIVALENT
INPUT NOISE
(Unweighted)
-78dBm,
typical,
(input shorted).
ATTACK
TIME**
(Time
to
reduce
signal
by
63%
of level
change)
15
milliseconds
for
10dB
level
change above
threshold.
5
milliseconds
for
20dB
level
change above
threshold. 3 milliseconds
for
30dB
level
change.
RELEASE RATE**
120dB/second
COMPRESSION RATIO
Continuously
variable
from
1:1
to 120:1
(infinity).
THRESHOLD
Continuously
variable
from
10mV(-38dB)
to
3V(+12dB).
INDICATORS
One
L.E.D.
indicator turns
"on"
to
show when
the input
level
is
below
set
threshold;
another
turns
"on"
when
the input
level
is
above
threshold.
A
steady-state,
sine-wave
tone exactly
at
the threshold voltage causes
both
L.E.D.'s to
remain dimly
illuminated.
METERING
Range
Function
Calibration
60dB
(-40dB
to
+20dB)
Switchable
for
input
level,
output
level
or gain change.
Rear
panel
potentiometer
sets
"OdB"
for
any
level
from
-10dB(250mV)
to
+10dB(2.5V).
POWER REQUIREMENTS
117V
AC, 50
or
60Hz.
8 watts
maximum.
'The wideband
distortion
figures
appear
to
suggest that
3rd-harmonic
distortion
is
dominant.
Thus,
an unweighted
T.H.D.
(Total
Harmonic
Distortion)
figure
would
be
similar to the
3rd-harmonic
value.
However,
the
specific
breakdown
of
distortion
is
more
informative.
3rd-harmonic
distortion
in
the
160
Series
decreases
linearly as
the
frequency
rises:
at
100Hz
3rd-harmonic
distortion
is
1/2 the
value at
50Hz,
etc.
•
'Attack
and
release rates
automatically vary with
rate
of change of
program
level
(attack
and
release rates
"track"
the
signal
envelope).
Specifications are subject to
change without
notice.