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12
A
REVIEW
Compr essor
A var iab
le
gain
ampl
ifier whose gain decreases
as
its input
level
increases past the threshold point
.
Limit er
A compressor with a
h igh
compress ion ratio; the high
ratio mainta ins
essentia
lly co nsta nt ou
t
p ut
level
desp ite any
increase in
in
put level above t
h
e
threshold.
Compression Ratio
Th
e
ratio, in dB, of input level
ch
ange above
threshold,
to outpu
t
leve
l
change. A compressor w hose output leve
l
changes 1dB for a
2dB
input level
cha nge has a 2:
1
Comp ress ion Ratio
.
Threshold
·25
·20
•
15
E
.0
..,
·
10
·
5
a=Una ltered Signal
Envelope
b=Enve
lope"a"
with
2: 1 Compression
c=Enve lope
11
a" wit
h
20:
1
Compression
T IM
E
>
T he
level
at w
h
ich compress ion begins
.
dbx Model 160
and Model 161 compressor/limiters
have adjustable
t
h
res-
ho
lds. Wh
en the
in
put level is be low the set
t
h
res ho ld, and
the
Outp
ut
Ga in contro
l
is set at " OdB" (12 o 'c lock), the
unit functions as a
1: 1
amp lifier (a unity gain device). When
t he input
leve
l
is above
the
set thres
h
old, the un
it
f
u
nctions
as a compressor, or as a limiter, depending
on
the com-
pression ratio selecte
d
.
Fig. 4
.
Attac
k
&
Release
T
im es "tr ack
" t
he envelop
e of
th
e in
pu
t
signal.
SPECI
FICATIONS-160
INPUT
Type
Actual
Impedance
Connector
Maximum Level
OUTPUT
Type
DISTORTION
*
Actu
al Imped
ance
Connector
Max. Level Bridging
(1
OK-o hm or greater Z)
Matching
(600 -ohms)
Output
Level
Adjust
(Continuous)
Protection
EQUIV
A
L ENT
INPUT
NOISE
(Unweighted)
ATTA CK TIME*
*
(Time
to reduce signal by 63% of level change)
REL EASE RATE**
COMPR ESSION RATIO
THRESHOLD
INDICATORS
METERING
Range
Funct ion
Calibration
POWER REQUIREMENTS
...
•
25
·
20
=>
•
15
0
·
1
0
·
5
1:
1 (Unity)
20
:
1
• 5
·
10
·
15
•
20 · 25
IN
Threshold
(Rotation point)
Fig.
5
-
Input and Outpu
t
L evel
s
at
various
compr ession
ratios.
Balanced
(differential)
transformerless.
50 K-o hms
(25K -ohms
when used
in
unbalanced mode, one side
tied to ground).
Jones-type
barrier
strip.
+2 1dB (8 .7V)
Single-ended, ground-compensated;
suitable for
driving
balanced o
r u
nbalanced loads.
25
ohms (typica
l
); w ill d
rive 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.
0.075
%
2nd
harmonic at infinite
compression
at
+4dBm
output
0.5
%
3rd harmonic typical
at
infinite compression ratio
-78dB
m
,
typical,
(input shorted)
.
15 mill iseconds for 1 Od B
level
change
above
threshold. 5 milliseconds for 20dB
level
change above threshold. 3 mi
lli
seconds for 30dB
level
change.
120dB/seco nd
Continuously
var iable from
1:
1
to
120: 1 (infinity).
Continuous ly variable
from
10mV(
-
38dB)
to
3V(+12dB)
.
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 thresho ld. A steady-state, sine-wave
tone exact ly at
the
threshold vol
t
age
causes both L.E.D.'s
to
rema
in
dimly illuminated.
60
dB (-4
0
dB to
+20dB)
Sw itchable
for input
level
, output
level
or gain change.
Rear pane
l
potentiometer
sets "OdB" for any level from
-
10dB(250mV)
to
+10dB(2.5V).
117
V AC, 50 or 60Hz. 8 watts maximum.
*The wi deband distortion
figures appear to suggest that 3rd-harmonic
distortion
is dominant.
Thus, an un weighted T.H.D. ( Total
Harmonic Distortion)
figure would be similar to the 3rd -harmonic value. Howe ver, the specific breakdown of distortion
is more
informati
ve.
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
subj ect
to change without
notice.
13