dbx 161 Instruction Manual - Page 2
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INTRODUCTION
The dbx
160
and 161 are single-channe
l
compressor/
limiters combining sophisticated technology and user-
oriented features in a compact package. Unique circuit
designs, such as true rms level-detection and feed-forward
gain reduction, place the 160 and 161 in a completely
different class from conventional compressor/limiters.
In
addition to increasing the stability and the available
range of compression, dbx's feed-forward approach makes
it
possible for the attack and release times to "track"
the
signal envelope. In conventiona
l
compressor/limiters,
the
attack and release times depend on feedback loop gain,
which means they constant ly must be readjusted for
optimum results at different compression ratios. Since the
attack and release t imes of dbx units vary automatically
with the rate of
level
change in the program materia
l
(the
envelope shape), operation is simplified; no manual attack/
release adjustments are required
.
At the same time, the
"naturalness"
of any given sound
is
better preserved.
The
dbx tec hnique of true rms level-detection gives you
audible benefits. Most compressor/limiters
use some form
of peak detection, with fast response characteristics that
can have a disturbing effect on program material. True rms
level detection closely simulates the response of the human
ear. Even at high compression ratios, the gain changing
action of the 160 Series is
highly
listenable and natural
sounding
.
Because of the unique feed-forward approach, dbx 160
and 161
I
imiters can achieve infinite compression with
comp lete stability and
inaudible
distortion. The dbx
approach is quite un
l
ike gain reduction in a conventional
compressor/limiter
.
Traditional
gain reduction is accom-
plished by sensing
signal
level at the device's output and
applying a correction signal, via a feedback loop. At
progressively higher compression ratios, the feedback
loop's
gain increases, distortion
increases,
and eventua lly instabi
li
ty
or oscil lation occurs. To avoid this problem, many con-
vent ional units
restrict
the maximum amount of feedback,
thus
restricting
the maximum compression ratio to some
lower
ratio,
such as 10:1 or 20:1. The dbx
160
and 161 are
free of the instability
of excessive
loop
gain, and can
provide infinite compression (approximate ly
120:
1 ).
GENERAL
INFORMATION
Models
The Model
160
is a fully professional compressor/limiter
with a balanced differentia
l
input, with an automatic
ground-loop compensated output (hum resulting from any
ground loop at the output
is
automatical ly sensed and
attenuated at least 40dB), and with a special protection
circuit that blocks
power
turn-on and turn-off
transients
from the output.
The Mode
l
161 is nearly the same as the
160,
but
is
priced for the smaller studio, or the semi-pro
user.
It has
the same advanced rms detection and feed-forward
circuitry as Mode
l
160, but it lacks turn-on/turn-off
transient
protection,
and ground-loop compensation. The
161
's
input
and output are unbalanced and terminated in
RCA-type phono jacks
.
Both models have adjustable thresho ld, and a pair of
LED's that
indicate
when the
input
level is above or below
the threshold. An il luminated meter displays a fu ll 60dB
range and
is
switchable to read input level, output level, or
gain
change.
The
meter's sensitivity is continuously
variable, so
"zero
VU" can be adjusted to equal your
system's nominal operating level, anywhere from +10 to
-1
OdB.
Output l ine level
is
also adjustable, ±20dB. Maximum
output on the 160 is
+26dB
( 1 5. 5 V)
into
a high impedance,
or
+24dBm
(12.3V) into 600 ohms. Maximum output on
the Model
161 is
+18dB (6.14V) into a
high
impedance, or
+
16dBm (4.89V) into 600 ohms.
Attractive ly styled and
functionally
designed, either
model can stand alone or can be mounted in a standard 19"
rack. Two
units
can be mounted side-by-side in
just 3½"
of panel space with the optional dbx RM-150-C rack mount
kit; the R M-150-D is for
rack
mounting of a sing le unit.
Applications
dbx noise reduction systems now make it possible to
process programs with 100dB, or greater, dynamic range.
Unfortunately,
in
some applications it
is
necessary to
restrict dynamic range. While dbx noise reduction systems
are used
in
the studio, for record production,
to maintain
wide dynamic
range,
th is range must often be restricted to
optimize the sound for broadcast and home playback. The
restriction of dynamic range is usually done with a com-
pressor, in the final stages of recording (or record master-
ing). In the broadcast field, where many stations compete
for an audience, a
high
average audio level can make a big
difference to radio station ratings. Compression is used to
attain
high
average
levels.
However, unless a high
-
quality compressor/limiter
is uti
l
ized, distortion
and
unwanted audible side-effects may degrade the sound
so badly that the advantages of high average level are
overcome, and audience interest can be lost. The 160
and 161 do a great job
in
both recording and broadcast
applications.
The
dynamic range of a
li
ve musical performance can be
even greater than 100dB. A high-quality compressor/
li
miter,
used judicious ly, can restrict the dynamic range, raise the
average
level,
help the operator avoid clipping distortion,
and improve the overall sound quality. Because the 160 and
161
sound so
natural,
they won't displease performers,
making them especially wel
l
suited to sound reinforcement
applications.
Compressor/ limiters can be useful in other applications
too.
The
160 and
161
are
ideal
for use as a high quality line
amplifier because of their low noise and distortion and high
output drive.
The
160 and
161
have the added advantage of
allowing you to conveniently dial
in
compression at any
time. In any application requiring
high-quality
compression
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