dbx 160 User manual

IND EX
INTRODUCTION
GENERAL INFORMATION
Models
App lications
Stereo Tracking
The Compressor asa Too l
FRONT PANEL CONTRO LS & METER ING
INSTALLATION
AC Power
Signal Connections
Input Impedance & Terminations
OPERATION
Power Switch
Thresho ld & Compression Ratio Adjustments
Output Gain Control Adjustment
Meter Calibration & Use
The 160 or 161 asa Line Amplif ier
A REVIEW
SPECIFICAT IONS 160
161
WARRANTY
FACTORY SERVICE
GLOSSARY
SCHEMATICS
ILLUSTRATIONS
Fig. 1 - Front Panel
Fig. 2A - Connecting the 160 in a Balanced Circuit
Fig. 28 • Connecting the 160 in an Unbalanced Circuit
Fig. 3A • Connecting the 161 in a Balanced Circuit
Fig. 38 · Connecting the 161 in an Unbalanced Circuit
Fig. 4 - Attack & ReleaseTimes "track" the envelope of the input signal
Fig. 5 · Input and Output Levels at various compression ratios
®
X Model 160/161
compressors/limiters
INSTRUCTIONMANUAL
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V11
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2
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 classfrom 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 times 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 technique 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 Iimiters can achieve infinite compression with
comp lete stability and inaudible distortion. The dbx
approach is quite unlike 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 eventually instabi lity
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 sensedand
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 Model 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 illuminated 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
-1OdB. Output line level is also adjustable, ±20dB. Maximum
output on the 160 is +26dB (15.5V) 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 RM-150-D is for rack mounting of a single 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 stagesof 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 lized, 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 live musical performance can be
even greater than 100dB. A high-quality compressor/ limiter,
used judicious ly, can restrict the dynamic range, raise the
average level, help the operator avoid clipping distortion,
and improve the overall sound quality. Becausethe 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 asa 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
3

4 or limiting the dbx 160 and 161 provide superior perfor-
mance at a reasonab le price.
Stereo Tracking
Some compressor/ limiters have jacks that ostensibly
equip the units for stereo operation. The jacks "strap" the
gain control sect ions of the two single-channel units
together so that the stereo image remains stable even when
the signa l level is radica lly different in the two channels.
dbx's Model 160 and 161, are not equipped for stereo
operation. The lack of "strapping" provisions is no over-
sight; it is a well thought out engineering dec ision. The
reason for this decision is simple, if not immediately obvious.
Stereo tracking between two separate compressor/ limiters
requires great accuracy. This tracking accuracy has little to
do with the quality or the ab ility of a single -channel unit to
meet its spec ifications . Even with better than average com-
ponent tolerances, component-to-component variation is
typically 10%; most potentiometers have 20% to lerances.
Such tolerances are perfectly acceptab le, and will.not
degrade the performance of an individual single-channel
un it. Internal trimmers are adjusted to provide any needed
correction, and any crit ical components are matched or
have prec ision tolerances.
While the front pane l settings of two "strapped" units
may be identical, component tolerances can cause the actual
performance to vary from unit to unit by as much as 20%.
Even small to lerance diffe rences will cause the stereo image
to shift rapidly from right to left. These normal component
tolerances on ly become a prob lem if two units are strapped
together for stereo operation.
If any given pair of single-channel units ever manufac-
tured could be strapped together for accurate stereo
tracking, individua l component tolerances in each un it
would have to be very tightly controlled . This approach
would not improve the performance of any one single-
channe l unit, but it would make the cost of all units
prohibitive.
There are three other ways to build compressors with
stereo strapping jacks: (The easy way out) Put in the jacks
on production units that are not critically matched, and
ignore the resulting prob lems : (The expensive way out)
insta ll highly accurate, precis ion components throughout
the compressor for accurate stereo tracking performance,
and charge every purchaser for the stereo capabi Iity, whether
or not it is needed, or (The hard way out for you) install
enough external tr im-pots so that, if you had the right test
equipment, you cou ld adjust the tracking accuracy
yourself ... as often as required by component aging or
touring abuse.
None of the above solutions were very palatable to dbx
(nor wou ld the resu lts have been to you, the user). dbx
decided that omitting the stereo tracking feature would
improve the overall value of the product, and wou ld help
dbx to keep its commitment to product excel lence at
reasonab le cost. Th ere is no reason for people who need
a single-channel compressor/limiter to pay for precision
parts or matching that they do not need. Neither is there
any reason for someone who needs a stereo compressor/
limiter to accept inferior performance from units with
strapping jacks but no matched or precision components
that would provide precise stereo tracking accuracy.
Instead, dbx decided to offer another model the 162
. ,
which is a two-channel compressor/ limiter designed and
bui lt for the user who needs precise stereo tracking. The
162 utilizes matched components and close-to lerance parts
to achieve precise tracking, with easy, single-knob adjust -
ments . The 162 does the job at an attractive price. It makes
a lot of sense when you thi nk about it: a precise dbx
compressor/limiter for single-channel jobs and another for
. . .
precise stereo operation.
The Compressor/Limiter as a Tool
Set up properly, a compressor can be a useful device.
Fi_gure4, Curve A shows the envelope of an input signa l
w1~h~o compression. (The "envelope" of a signal is a graph
of its instantaneous level.) Curve B shows the envelope of
the same signa l after 2: 1 compression has reduced its level.
Cur~e. C shows the results of extreme 20: 1 compression
(l1m1t1ng).At this extreme compression ratio, the output
level is essentially constant for any input above the
threshold.
misused. In fact, many people refuse to use compress ion
even when it wou ld improve the audio qual ity, because they
have heard compression being misused all to often . One of
the nicest aspects of dbx compressor /Iimiters is the fact that
th~y are easy to use and they sound better than competitive
units ... even when using more extreme compression.
Much of the character of music is contained be low the
attacks or peaks. If the threshold is set 1OdB or more above
the average level of the input signa l, then compression will
take place primari ly on the uppermost peaks or attacks of
the signal, minimizing musica l alteration. However if the
threshold is set to a level that is lower with respect to the
average level, noticeable musica l alteration may occur.
With a 2: 1 compression ratio, a 2dB increase in input
le~el (above threshold) causes the output to rise only 1dB.
With a 4:1 ratio, a 4dB increase at the input results in a 1dB
increase at the output. With a 10: 1 ratio, a 1OdB increase
at the input resu lts in a 1dB increase at the output, and so
forth. Therefore, the amount of musical alteration also
depends on the compression ratio used, as wel l as the
th reshold setting.
Music listen ing pleasure is greatest with ful l una ltered
dynamic range. Because dbx noise reduction systems afford
a useab le dynam ic range of over 1OOdB,dbx recommends
their use whenever practical. Limiting or compression can
be used in conjunction with dbx noise reduction systems
for effect on ly. '
A compressor/limiter, as with any useful tool, can be
5

6
FRONT PANEL CONTROLS & METERING*
Fig. 1 -Front Panel
COMPRESSION control varies the
amou nt of compression fro m 1:1 (unity
gain) up to infini ty (approx. 120: 1).
Th e unit can be considered to be
limiting at compression settings of
OUTPUT GAIN control adjusts the gain of the
unit's output stage; can actually attenuate up to
20dB, or can provide up to 20dB of gain. This
control is independent of Threshold and
Compression.
10:1 or higher.
BELOW, ABOVE THRESHOLD (L .E.D.'s)
When the amber indicato r is illuminated, the
input level to the compressor /limi ter is below
the threshold level adjusted by the
THRESHOLD control. When the red indi-
cator is illum inated , the inpu t level to the
compressor /limiter is above the thresho ld level.
The L.E.D.'s do not measure output level.
TH RESHO LO control adjusts the level
above wh ich compression or li mi ti ng
occurs, and is continuously variable
from 1OmV to 3 volts.
1V
3V
POWER
2
1.5 1
t
6
-10
10
20 - 20 • 20
(D GAIN
INPUT OUTPUT CHANGE
i i I
I
METER dbx
COMPRESSOR/LIMITER
POWER switch turns AC
power "on" and "off". No
signal flows when power
METER FUNCTION
SWITCHES select whether
the rneter displays th e
INPUT level, the OUT -
PUT level, or the amount
of GA IN CHANGE .
METER
Factory set for OVU =+4dB, the meter can
be recalibrated to other nom inal OVU levels
(+20 to -10dB). The meter calibration
trimmer is on the rear panel (the screw
beneath the meter face is a zero-set adjust-
ment to assure the needle rests at OVU when
the uni t is "off"}.
is "off".
•controls and functions are identical for the Mod el 160 and Mod el 161.
INSTALLATION
The units are supplied in handsome cabinets that can be
placed almost anywhere . Self-adhesive rubber feet are
supplied for protection of delicate finishes that might
otherwise be marred by the compressor/limiter's wood
cabinet. Avoid mounting a unit above any source of heat
or strong electro-magnet ic fields, such asthose generated
by power amplifiers or vacuum tube equipment. Two dbx
compressor/limiters can be mounted side-by-side in a
standard 19-inch rack with a dbx Rack Mount Kit RM-
150-C, or asingle unit can be rack mounted in a 19" rack
with a dbx Rack Mount Kit RM-150-D.
AC Power
Connect the Model 160 or 161 to a 117V AC, 50 or 60Hz
AC power source only. Models for use with foreign power
sources are available. Contact the dbx factory for informa-
tion. The Model 160 or 161 requires 8 watts of AC power
(Maximum). As a precaution, do not connect the AC power
cable unti l all signal connections have been made.
Signal Connections
MODEL 160
Make input and output connections to the barrier strip
on the rear panel, asshown in Figure 2. Note that the 160's
input impedanc e is 50k -ohms when connected in the
"balanced" mode, but is 25k-ohms if connected in an
unbalanced configuration. When using an unbalanced input
connection, reversing the "+" and "-" input terminals will
causethe output signal to be 180 degreesout-of-phase with
the input signal.
When the output is connected to an unbalanced load,
special circuits in the 160's output stage senseany ground -
loop current (hum). The ground-loop compensation then
appl ies a precise correction signal to the 160 output, at the
proper level and phase to reduce hum in the output signal
by up to 40dB. For maximum hum reduction, avoid com-
mon grounding at the inp ut and output (avoid "double-
grounding"). One grounding method that usually works is
to ground the shield at the 160's output "Gnd" terminal
and also ground it at the input of the following device. Do
not connect the shield at the 160' s input "Gnd" terminal.
Leave the input shield connect ed only to the output of
device feeding the 160.
NOTE: Connec ti ng the "-" and "shield" leads together at the
160's output, instead of at the input of the following device,
defeats th eground-loop compensation circuitry.
7

8
TIP/RING /SLEEVE
PHONE
PLUG
T HIG H
v R 0LOW
•
S , SHIELD
XL
CONNECTOR
3
I
dbx
HIGH
LOW
Ml TUI
ca1,.1e114r,o-.r
•
SHIELD
MOOH 160
I'"""''-.
r00tr'O'..
• •
• •
• - 0 ~ 0
HIGH
LOW
-,- SHIELD (GND)
XL
CONN ECTOR
3,,.-- --- 2
TIP/RING/SLEEV E
PHONE
PLUG
HIGH • T
LOW • R V
SHIELD , S
RECOMMEND NOT
CONNEC TING THE
SHIE LD HERE
(UNLESS HUM
DEVE LOPS)
\ 1 /
RECOMMEND
CONNECT ING THE
SHIELD HERE
Fig. 2A • Connecting the 160 in a Balanced Circuit
STD. RCA
PIN
dbx
M{T OI
CAl,.1.IIIAl!ON
•
r,~....,,-,ou,~u,.
• •
• •
•-o• - o
PHONE PLUG
PLUG
T
I V •
s •
HIGH
SHIE LD HIGH (SIGNAL!
SHIELD (GROUND!
\
USE SINGLE -CONDUC TOR
SHIE LDED CABLE
Fig. 28 - Connecting the 160 in an Unbalanced Circuit
MODEL161
The 161's input and output are unbal anced, term inating
in RCA pin jacks. Th us, it has no ground -loop comp ensation
circuitry. Make signal connectio ns to the 161 asshown in
Figure 3.
TIP/A ING/SLEEVE
PHONE
PLUG
T HIGH
v R • LOW
• SLD
XL
CONNECTOR
2 3
1
Fig. 3A · Connecting the 161 in a Balanced Circuit
STD. RCA
PHON E
PLUG PIN
PLUG
I T HIGH
•
s SHIELD
Fig. 38 · Connecting the 161 in an Unbalanced Circuit
dbx "~" OUll'VI
Ml 1(11 1 ~ @
Co\ll.ftAU(I._.
•
I
I
I '
MOOtil 1'1
A LWAYS "TIE'" "T IE" SH IELD &
SHI ELD & LOW LOW HERE IF
CONNECTORS HUM DEVELOPS
HERE /
' USE DUAL -CON DUCTOR
"" SHIE LDED CABLE
dbx INl'Ut
MfTUII @ 1)
CAllil:IJIArl(>•,
•
HIG H
SHIELD
(COMMON)
MODEL 161
HIGH
SHIELD
(COMMON)
"" SINGLE-CONDUC TOR _/
SHIELDED CAB LE /
MODEL 160
HIGH
l w
RCA
PIN
PLUG
HIGH 0
LOW T
SHIELD (GNDI \ SHIELD
USE DUAL -CONDUC TOR
SHIELDED CABL E & "T IE"
THE LOW & SHIELD
TOGETHER AT THIS POINT
XL
CONNECTOR TIP /RING /SLEEVE
PHONE
PLUG
RCA
PIN
PLUG
3 /""-
1
HIGH T
LOW • RV
S D • S
0
STD.
PHONE
PLUG
HIGH T I
• V
•
SHIELD S
STD .
PHONE
PLUG
T I
V
s
9

10 Input Impedance & Terminations
There is sometimes a misunderstanding regarding the
nature of matching and bridging inputs, the useof termi-
nating resistors, and the relationship between actual input
impedance and nominal source impedance. Most electronic
outputs work well when "terminated" by an input (con-
nected to an input) having the same or a higher actual
impedance. Outputs are usually overloaded when
terminated by an impedance that is lower than the source
impedance. When the input impedance is nearly the same
impedance asthe source, it is known asa "matching" input.
When an input is 10-times the source impedance, or more,
the input is considered to be a "bridging" input.
The dbx 160 and 161 have respective actual input
impedances of 50,000 ohms and 25,000 ohms (they are
high-Z* inputs) . This makes the dbx inputs suitable for use
with virtually any nominal source impedance, low or high.
The dbx inputs wil l bridge 150-ohm or 600-ohm (low-Z)
lines, and will match 10,000-ohm or greater impedance
(high-Z) lines, It seldom is necessary to place a 600-ohm
"terminating resistor" acrossthe input of the dbx unit. In
fact, most 600-ohm outputs operate normally when
bridged by a high impedance; it is asthough no load were
connected to the source device. The only instance where a
term inating resistor may be required is when the manu-
facturer of the source device specifica lly states that a
terminating resistor is necessary. In such cases,there is
usually a special type of output transformer in the source
device, and the terminating resistor assuresoptimum
frequency response in that device. Terminating resistors
are not needed for the dbx unit to operate correctly. If a
150-ohm or 600-ohm resistor is specified for the source
device, it should be installed at the end of the cable nearest
the dbx unit in order to minimize possible hum, noise or
signal lossesin the cable.
*"Z" is an accepted abbreviation for "impedance."
OPERATION
Power Switch
Depressthe "Power" switch for the 160 or 161. The
"BELOW THRESHOLD" LED and the meter lamps should
illuminate. It is normal for the "ABOVE THRESHOLD"
LED to flicker with no input signal applied during the time
when the power is turned on or off.
Threshold & Compression Ratio Adjustments
INITIAL CONTROL SETTINGS
THRESHOLD fully clockwise (3V), OUTPUT GAIN
at "12 o'clock" (OdB). COMPRESSION RATIO at the
appropriate ratio, low settings for compression (1:1 to 4: 1
l.
high settings for limiting (10: 1 to infinity).
PROCEDURE
App ly normal-level program material to the input. The
BELOW THRESHOLD LED wi ll remain on, except when
input levels exceed the threshold setting. The ABOVE
THRESHOLD LED indicates when compression is taking
place. Starting with the TH RESHOLD fully clockwise,
rotate it counterclockwise until the ABOVE THRESHOLD
LED begins the flicker. At this setting, compression will
begin whenever the input level exceeds the threshold setting.
Further counterc lockwise rotation of the THRESHOLD
control wi ll causecompression to begin at a lower point
relative to the maximum input level.
For a further discussion of the useof the COM-
PRESSION RATIO, and THRESHOLD controls, refer to
the final section of this manual, "COMPRESSION RATIO,
A REVIEW."
NOTE: The 160's ground-loop compensation circuitry
and power turn-on turn-off transient protection circuitry
operate norma lly at any settings of front panel controls.
Output Gain Control Adjustment
When the 160 or 161 is used as a com pressor, OUTPUT
GAi N can be used to increase overall level that is partially
decreasedby compression. The effect is to raise the average
level of the program material, whi le decreasing its dynamic
range. To increase the gain, rotate the OUTPUT GA IN
control clockwise past the "OdB" position; to decreasethe
gain, rotate the control counterclockwise.
THRESHOLD fully clockwise past the 3V position, and
set COMPRESSION RATIO comp letely counterclockw ise,
(to the "1: 1" position). Connect an accurate, VU-reading
voltmeter to the 160 or 161 output terminals, and adjust
the OUTPUT GAIN control to produce a reading on the
outboard meter that is identica l to the input level. Then,
depressthe meter OUTPUT button on the front panel. If the
160 meter still reads"OdB", the unit isproperly calibrated.
Audio signals often have peaks that are 20dB above VU
meter readings (VU meters indicate averagelevels). Even
when compressed at a 2: 1 ratio, such peaks can stil l reach
10dB above VU-indicated levels. To avoid clipping, usean
averageinput level, such as-10 to +8dB, that is below the
maximum specified input levels (+21dB for the 160, +17
dB for the 161). When the COMPRESSION RATIO is set
at a low factor*, extreme clockwise rotation of OUTPUT
GAIN may cause the 160 or 161 output stage to cliP
program peaks ... even when maximum input levelsare
not exceeded.
Due to the fact that 20dB of gain can be added in the
160 or 161's output stage, raising the output level
substantia lly above the input level may cause clipping.
It is suggestedthat, for normal operation, OUTPUT
GAIN be set at 12 o'clock (OdB) position.
Meter Calibration & Use
The meter in •the 160 and 161 is factory calibrated to
read "O" at +4dB (1.23V) output level. To recalibrate the
meter, depressthe INPUT LEVEL meter function switch.
Feed a 1kHz signal, at your selected nominal operating level
(the level desired for a "O" meter reading) to the com-
pressor/limiter input. Then adjust the 160 or 161 meter
calibration control (on the rear panel) until the meter
indicates "OdB". To check the meter calibration, rotate
*The term "factor" refers to the compression ratio.
The 160 or 161 asa Line Amplifier
To useeither model asa line amplifier, adjust COM-
PRESSION RATIO to its maximum counterclockw ise
position ("1 :1"), THRESHOLD to its maximum clockwise
position ("3V"), and OUTPUT GAIN to whatever setting
is needed for the application. Remember that, aswith any
amplifier, excessive gain may cause output clipping of high-
level signals (see"Output Gain Contro l Adjustment" in
preceding paragraphs). To add compression, adjust the
COMPRESSION RATIO and the TH RESHOLD to the
desired settings.
11

12
A REVIEW
Compr essor
A variable gain ampl ifier whose gain decreases as its input
level increases past the threshold point .
Limit er
A compressor with a high compress ion ratio; the high
ratio mainta ins essentia lly co nsta nt output level desp ite any
increase in input level above the threshold.
Compression Ratio
The ratio, in dB, of input level change above threshold,
to outpu t level change. A compressor whose output level
changes 1dB for a 2dB input level cha nge has a 2: 1
Comp ression 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
TIME >
The level at which compress ion begins . dbx Model 160
and Model 161 compressor/limiters have adjustable thres-
ho lds. When the input level is below the set threshold, and
the Outp ut Gain contro l is set at " OdB" (12 o'clock), the
unit functions as a 1: 1 amp lifier (a unity gain device). When
the input level is above the set thres hold, the un it functions
as a compressor, or as a limiter, depending on the com-
pression ratio selecte d.
Fig. 4 . Attac k & Release Times "tr ack" the envelope of
th e input signal.
SPECIFICATIONS-160
INPUT Type
Actual Impedance
Connector
Maximum Level
OUTPUT Type
DISTORTION *
Actual Imped ance
Connector
Max. Level Bridging
(1OK-ohm or greater Z)
Matching
(600 -ohms)
Output Level Adjust
(Continuous)
Protection
EQUIV ALENT 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
· 10
· 5
1: 1 (Unity)
20 : 1
•5 · 10 · 15 •20 · 25
IN
Threshold (Rotation point)
Fig. 5 - Input and Outpu t Levelsat various compr ession ratios.
Balanced (differential) transformerless.
50 K-ohms (25K -ohms when used in unbalanced mode, one side tied to ground).
Jones-type barrier strip.
+21dB (8.7V)
Single-ended, ground-compensated; suitable for driving balanced or unbalanced loads.
25 ohms (typica l); w ill 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.
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 1OdB level change above threshold. 5 milliseconds for 20dB level
change above threshold. 3 mi lli seconds for 30dB level change.
120dB/seco nd
Continuously variable 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 voltage causesboth L.E.D.'s to remain dimly illuminated.
60dB (-4 0dB 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).
117V AC, 50 or 60Hz. 8 watts maximum.
*The wideband 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 decreaseslinearly 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.
13

14
SPECIFICATIONS - 161
INPUT
OUTPU T
DISTORTION*
Type
Actual Impedance
Connector
Maxim um Level
Type
Actual Impedance
Connector
Max. Level Bridging
(10 K-ohm or greater Z)
Matching
(600-ohms)
Output Level Adjust
(Continuous)
EQUI VA LEN T INPUT NOISE
(Unweighted)
ATTACK T IME**
(Time to reduce signal by 63% of level change)
RELEASE RAT E**
COMPRE SSION RATIO
TH RESHOLD
IN DIC ATORS
METERI NG Range
Function
Calibr ati on
POWER REQUIRE MEN TS
Unbalanced
25K-ohms
RCA pin jack (phono connector).
+17dB (5.5V)
Unbalanced
100 ohms (typical); wi II drive low or high-Z loads.
RCA pin jack
+18d8 (6.16V)
+16d8m (4.9V)
+20dB from unity gain point.
0.75% 2nd harmonic at infinite
compression at +4dBm output
0.5% 3rd harmonic typical at
infinite compression ratio
-78dBm, typical, (input shorted).
15 milliseconds for 10d8 level change above threshold. 5 milliseconds for 20dB level
change above threshold. 3 milliseconds for 30d8 level change.
120dB/second
Continuously variable from 1: 1 to 120: 1 (infinity!.
Continuously variable from 10mV(-38dB) to 3V(+12d8).
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 causesboth L.E.D.'s to remain dimly illum inated.
60d8 (-40dB to +20d8)
Switchable for input level, output level or gain change.
Rear panel potentiometer sets "OdB" for any level from - 10dB(250mV) to +10d8(2.5V).
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 decreaseslinearly as the frequency rises: at TOOHz 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.
dbx PRODUCT WARRANTY
All dbx products are covered by a Limited Warranty.
Consult your warranty card or loca l dealer for deta ils.
FACTORY SERVICE
The dbx Customer Service Department is prepared to
give add itional assistance in the use of th is product. All
questio ns regarding inter facing dbx equipment with your
system, service informa tion or info rmation on special
applicat ions will be answered . You may cal l during
normal business hours - Telephone: [phone] or
write to: dbx, Inc.
71 Chapel Street
Newton , MA 0219 5
Attn : Customer Service Department
Should it become necessary to have your equ ipment
factory serviced;
1. Please repack the unit including a note desc ribing
the problem along with the day, month and year of
purchase.
2. Send the un it freight prepaid to:
dbx , Inc.
224 Calvary Street
Waltham , MA 02154
Attn : Repair Departm ent
3. We recommend that you insure the package and
send it via United Parce l Service wherever poss ible.
4. Please direct all inqui ries to the dbx Customer
Service Department .
Outs ide the United States - contact your neares t dbx
dealer for the name of an authorized repair ce nter.
15

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GLOSSARY
Asperity No ise
This is a swishing type of background noise that occurs with tape
recordings in the presence of strong low frequency signals, especially
when there are no high frequency signals to mask the hiss. Asperity
noise is caused by minute imp erfections in the surface of the tape,
includ ing variations in the magnetic particle size in the tape's oxide
coating. The imperfections inc reaseor decrease the strength of the
magnetic field passing the play head in a random manner, resulting
in audible noise. Asperity noise may be present even when no
program is record ed. When a program is recorded, asperity noise
becomes superimposed on the signal, creating modu lated asperity
noise, or "modulation noise." Using high-quality tape with a
calendered surface helps reduce asperity and modulation noise
(calendered tape is pressed smooth by high-pressure rollers).
Attack Tim e
Attack time may mean different things, depending on the
context. In music, the time it takes for a note to reach its full
volume is the attack time of the note . Percussive inst ruments have
short attack times (reach maximum volume quickly) and wind
instruments have long attack times (reach maximum volume more
gradually).
When a compressor (or expander) changes the level of an incom-
ing signal, the circuitry actually requires a finite amount of time to
complete that change . This time is known as the attack time. More
precisely, the attack time is the interval (usually measured in milli -
seconds or microseconds) during which the compressing or expand-
ing amp lifier changes its gain from the initial value to 63% of the
fi nal value.
Aux Input (Aux Level)
Aux inputs, an abbreviation for auxi liary inputs, are low
sensitivity jacks provided on most hi-ti and semi-professional
equipment. Aux inputs (also known as "aux level" or "line level"
inputs) have "flat" frequency response and are intended to be used
with preamp lified signals. Aux-level (line-level) signals are medium-
level, higher than micropho ne levels, but not enough pow er to
drive a speaker. The advantage to these levels is that they are less
susceptible tci hum and noise than are microphone levels. Typical
items which might be connected to aux inp uts are tape machine
"play" outputs, tuner outputs, and dbx "play" outputs. Mic-level
or phono-level signals are considerably lower in level than aux inp uts
(approx. -60 to -40dBV), so they will not produce adequate volume
when connected to an aux input. Moreover, phono cartridge outputs
require R IAA equal ization which is not provided by aux inputs.
Bandwidth
Bandwidth refers to the "space" between two specif ic
frequencies which are upper and lower limits; alternately, band-
width refers to the absolute value of the range of frequenc ies
between those limits. Thus, a filter which passesfrequencies from
1,000Hz to 1O,OOOHzmay be said to have a bandwidth of 1kHz •
10kHz, or it may be said to have a 9kHz bandwidth (10kHz minus
1kHz equals 9kHzl.
Bandwidth is not necessarily the same as frequency respo nse.
Bandwidth may be measured at low levels, and frequency response
at higher levels. Moreover, bandwidth may refer only to certain
portions of the circuitry within a piece of equipment, whereas
frequency response may refer to the overall performance of the
equipment. Thus, while the overall input-to-output frequency
response of dbx type 11equipment is 20Hz to 20kHz, the band-
width of the RMS detection circuitry within that equipment is
30Hz to 1OkHz.
Bass
The low audio frequency range below approximate ly 500Hz.
For the purpose of discussion or analysis, the bass range may be
further div ided into upper bass (250 to 500Hz), mid bass
(100-200Hz), low bass (50-1 OOHz), and ultra- low bass (20-50Hz).
BassBoost
An accentuat ion of the lower aud io frequencies (bass frequen-
cies), whereby they are made louder than other frequencies.
Biamplified
Descriptive of a sound system which uti lizes a low level cross-
over network to divide the fu lI-spect rum audio signal into low and
high frequency ranges. These ranges are then fed to separate
power amplifiers, which in turn feed low frequency speakers
(woofers) and high frequency speakers (tweeters).
Bias
Bias, as the term is used in tape recording, is a very high fre-
quency signal (usually over 1OOkHz) that is mixed with the
program being recorded in order to achieve Iinear magnetization of
the tape. If only the audio program were applied to the recording
head, a very distorted recording would result because lower-energy
portions of the program would not be able to overcome the initial
magnetization threshold of the tape (known as hysteresis).
The frequency of the bias signal is not critical, so long as the
record and erase bias are synchronized. However, the bias
energy level has a direct effect on the recorded level, background
noise, and the distortion. It is sometimes necessary to reset the bias
level for optimum performance with different types of recording
tape, and professional tape machines are equipped with continu-
ously variable bias controls; many consumer tape machines are now
equipped with bias selector switches .
achieved with a compressor, a special type of ampl ifier that
decreases its gain as the level of the input signal inc reases. The
amount of compression is expressed as a ratio of the input dynamic
range to the output dynamic range; thus, a compressor that takes
Clipping
Clipping is a very distorted sound. It occurs when the output
capabilities of an amplifier are exceeded, and the amp can no longer
produce any more voltage, regardless of how much additional gain
or how much more input signal is present. Clipp ing is relatively easy
to see on an oscilliscope, and it is sometimes audib le as an increase in
harmonic distortion. In severe casesof clipping (hard clipping),sine-
waves begin to resemble square waves, and the sound quality is very
poor. Often, the maximum output level of an amplifier is defined
as that level where clipping begins to occur. There is a phenomenon
known as input clipping , and this may occur where the input signal
is so high in level that it exceeds the level-handling abi lity of the
transformer and/or of the input amplifier. Clipping also occurs
when tape is saturated by excessive record levels.
So-called "soft clipping" is usually the result of transformer
saturation, and it may be somewhat lessobjectionable than the
"hard clipping" that occu rswhen output voltage lim its are reached.
Aside from degrading the sound quality, clipping can damage loud•
speakers. Output clipping may be avoided by reducing the level of
the input signal, reduci ng the gain of the amplifier, or using a
larger amplifier. Input clipping may be avoided by reducing the
level of the incoming signal, and then increasing the gain of the
amp li fier.
Clipping Level
This is the signa l level at which clipping just begins to occur.
Clipping level is not always easy to define. It may be a matter of
visually judging the waveform on an oscil liscope as the level is
increased; alternately, cl ipping level may be defined as the level at
which harmonic distortion reaches a given value. Tape clippi ng, or
saturat ion , is defined as the 3% harmonic distortion level.
Compression
Compression is a process whereby the dynamic range of program
material is reduced. In other words, the difference between the
lowest and highest audio levels is "squeezed" into a smaller dynamic
range. A compressed signal has higher average level, and therefore
may have more apparent loudness than an uncompressed signal,
even tho ugh the peaks are no higher in level. Compression is
a program input with 1OOdB of dynamic range and yields an output
program of 50d B dynamic range may be said to have a 2: 1 com-
pression ratio .
Compressor
A compressor is an amp li fier that decreases its gain as the level
of the input signal increases to reduce the dynamic range of the
program (see "compression"). A compressor may operate over the
entire range of input levels, or it may operate only on signals above
and/or below a given level (the threshold level).
Crossover Frequency
In loudspeaker systems and mult i-amp lifier audio systems, the
transition frequency (actua lly a frequency range) between bass and
midrange or midrange and treb le speakers or amp lifiers.
Crossover Network
A circuit which divides the audio spectrum into two or more
frequency bands for distr ibution to different speakers (high level
crossover) or different amp lifiers which then feed different
speakers (low level crossover).
High level crossovers are usually built into the speaker cabinet,
and are passive (they requ ire no power supply) . Low level cross•
overs are used in biamplified or triamp lified sound systems . They
are usually self-contained, and come before the power amplifie rs.
Low level crossovers may be passive or act ive; active low level
crossovers are known as "electronic crossovers."
Damping Factor
The ratio of loudspeaker impedance to the amplifier's output
source impedance. Damping describes the amplifier's ability to
prevent unwanted, residual speaker movement. The higher the
numerical value, the better the damping.
DB (Decibel) also, dBv dBV dB SPL dBm dB
One dB is the smallest change in loudness the average human ear
can detect. OdB SPL is the thresho ld of human hearing whereas the
threshold of pain is between 120 and 130dB SPL. The term dB is an
abbreviation for decibel, or 1/1Oof a Bel. The decibel is a ratio, not
an absolute numb er, and is used to express the difference between
two power, voltage or sound pressure levels. (dB is 1Otimes the
logarithm of a power ratio or 20 times the logarithm of a voltage
11

111 or sound pressure ratio.) if the number of "dB's " are referenced
to a given level, then the value of the dB number becomes spe-
cific.
or "breathing" effects, whereas very slow decay times may cause
moderate-level program which follows high- level program or pro-
gram peaks to be too low in level.
dBV expresses a voltage ratio. OdBV is usually referenced to
1.0V RMS. Thus OdBV =1V RMS, +6dBV =2V RMS,
+20dBV =10V RMS, etc.
Decoder
When a circu it restores an original program from a specially
treated version of that program, the circuit may be said to decode
the program . The equ ipment or circuit which performs this
function is known asa decoder. Decoders must be used only with
programs which have been encoded by complementary encoding
circuitry. Typical decoders include: FM tuners that use multiplex
decoders to extract left and right stereo signals from left -plus -right
and left -minus -right signals, matrix quadraphonic decoders that
extract four channels of program from the stereo program on
encoded recordings, and dbx decoders that retrieve wide-dynamic
range programs from the compressed programs on dbx -encoded
recordings.
dB SPL expresses a Sound Pressure Level ratio. dB SPL is a
measure of acoustic pressure (loudness), not acoustic power,
which would be measured in acoustic watts . OdB SPL is
equal to 0.0002 dynes/square centimeter (the threshold of
human hearing at 1kHz). As with dBV, an increase of 6dB
SPL is twice the sound pressure, and an increase of 20dB SPL
is an increase of 10 t imes the sound pressure.
dBm expresses a power ratio. OdBm is 1 milliwatt (.00 1
watts), or 0.775V rms delivered to a 600 -ohm load . +3
dBm =2 milliwatts, or 1.096V into 600 ohms (V2times OdBm),
+10dBm=10 milliwatts, or 2.449V into 600 ohms (3 .16 times
OdBm ), etc. dBV and dBm differ by 2.21 when deal ing with
600-ohm circuits. However, when the impedance is other
than 600 ohms , the value of dBV remains the same if the
voltage is the same, whereas the value of dBm decreases with
increasing impedance.
De-emphasis & Pre-emphasis
De-emphasis and pre-emphasis are related processes that are
usually done to avoid audio noise in some storage or transmission
medium. Pre-emphasis is a boost at specif ic higher frequenc ies, the
encoding part of an encoding/decoding system. De-emphasis is an
attenuat ion at the same frequencies, a reciprocal decoding that
counteracts the pre-emphasis. In dbx noise reduction, de-emphasis
is performed by the decoder (the play circuitry). The de-emphas is
attenuates high frequencies, thereby reducing tape modu lation
noise and restoring the original frequency response of the program
before it was dbx encoded. There are other types of pre-emphasis
and de-emphasis. For examp le, in FM tuners, de-emphas is is used
to compensate fo r special equali zation (known as 75-microsecond
pre-emphasis) applied at the stat ion's transm itter.
dB alone, without any suffix, doesn't mean anything un less
it is associated w ith a reference. It may express the differ -
ence between two levels. Thus, the difference between
1OdBV and 15dBV, the difference between OdBm and
5dBm, and the difference between 90dB SPL and 95dB
SPLare alI differences of 5dB.
Decay T ime
Dynamic Range
Decay time may mean different things, depending on the con-
text. A compressor's decay time is also known as its release time
or recovery time. After a compressor (or expander) changes its
gain to accommodate an incoming signal, and the signal is then
removed, the decay time is the amount of time required for the
circuitry to return to "normal." More precise ly, the decay time
The dynamic range of a program is the range of signal levels
from the lowest to the highest level. In equipment, the dynamic
range is the "space," in dB, between the residual noise level and
the maximum undistorted signal level. A program with wide
dynam ic range has a large variation from the softest to the loudest
passages,and will tend to be more life li ke than programs with
narrow dynamic range.
Encod er
is the interva l (usually measured in microseconds or milliseconds)
during which the compressing or expanding amplifier returns to
90% of the norma l gain. Very fast decay times can cause "pumping" When a circu it processes an orig inal program to create a
specially treated version of that program, the circu it may be said
to encode the program. T he equipment or circuit which performs
this funct ion is known as an encoder. Encoded programs must
decoded only with complementary decoding circu itry. Typical
encoded programs include: FM multip lex broadcasts, matrix
quadraphonic recordings, and dbx encoded record ings.
Envelope
In music, the envelope of a note
describes the change in average signal
level from initial attack , to peak level,
to decay time, to sustain, to release
time. In other words, the envelope
describes the level of the note as a
function of time. Envelope does not Thtouth ntt,stheenn lOPt,
refer tQ frequency. 1he s19nllo1n w1th1n th• envelop e,
In fact, any audio signal may be said to have an envelope.While
all audio frequencies rise and fall in instantaneous level from 40 to
40,000 times per second, an envelope may take many mi lliseconds,
seconds or even minutes to rise and fall. In dbx processing, the
envelope is what "cues" the rms level detection circuitry to com -
press and expand the signal; the peak or average level of ind ividual
cycles of a note would be useless for level detection because the
gain wou ld change much too rapidly for audibly pleasing sound
reproduct ion.
EQ {Equalization)
EQ or equalization, is an intentional change in the frequency
response of a circuit. EQ may be used for boosting (increasing) or
cutting (decreas ing) the relative level of a port ion of the aud ible
spectrum. Some EQ is used for achieving sound to suit persona l
listening tastes, whi le other types of EQ are specifica lly designed
to correct for non -Iinearities in the system; these correct ive EQ
"curves" include tape (NAB or CCIR) equalizat ion, and phono-
graph (RIAA) equalization. In a sense, the pre-emphasis and de-
emphasis used in dbx processing are special forms of equalization.
There are two common types of EOualization curves
(characteristics): PEAKING and SHELVING. Shelving EQ is
used in most Hi -Fi bass and treb le tone contro ls. Peaking EQ is
used in Hi-Fi midrange tone controls, in graphic equalizers, and
many types of professiona l sound mixing equ ipment.
EQ is performed by an equalizer, which may be a special ly built
piece of equipme nt, or it may be no more than the tone contro l
section of an amp lifier. Graphic equalizers have many contro ls,
each affecting one octave, one-half octave, or one-third octave of
the audio spectrum. (An octave is the interva l between a given tone
and its repet ition eight tones above or below on the musical scale;
a note which is an octave higher than another note is twice the
frequency of the first note.)
Expander
An expander is an ampl ifier that increases its gain as the level of
the input signal increases, a characteristic that "stretches" the
dynamic range of the program (see "expansion"). An expander may
operate over the entire range of input levels, or it may operate only
on signals above and/or below a given level (the thresho ld level).
Expansion
Expansion is a process whereby the dynamic range of program
material is increased. In other words, the difference between the
lowest and highest audio levels is "stretched" into a w ider dynamic
range. Expansion is sometimes used to restore dynamic range that
has been lost through compression or limiting done in the original
recording or broadcast; expansion is an integral part of com -
pander-type noise reduction systems, including dbx. Expansion is
achieved with an expander, a special type of amplifier that increases
its gain as the level of the input signal increases. The amount of
expans ion is expressed as a ratio of the input dynam ic range to
the output dynamic range; thus, an expander that takes a program
input with 50d B of dynamic range and yields an output program
of 1OOdB dynamic range may be said to have a 1:2 compress ion
ratio.
Fund amental
A musical note is usually comprised of a basic frequency,
plus one or more whole- num ber mu ltip les of that frequency.
The basic frequency is known as the fundamenta l, and the
mult ipl es are known as harmonics or overtones. A pure tone
would cons ist of only the fundamental.
Ground Compens ated Output
This is a sophist icated output circuit that senses the potential
difference between the ground of the dbx unit and the shield
ground of unbalanced inputs to which the dbx unit is connected.
Ideally, the dbx unit and the input of the following device should
be at the same level (potential). However, where grounding is not
"right" (where so-called "ground loops" exist), this circuit calculates
the ground error and adds a correct ion signal to the high side of the
output, thereby cancel ling much of the hum, buzz and noise that
might otherw ise have been introduced by ground loops.
IV

V Harmonic Distortion
Harmonic distortion consists of signal components appearing
at the output of an amplifier or other circuit that were not present
in the input signal, and that are whole-number mu lti ples (harmonics)
of the input signal. For examp le, an amplif ier given a pure sine-
wave input at 100Hz may produce 200Hz , 300Hz, 400Hz, 500Hz,
600Hz and even 700Hz energy, plus 1OOHz, at its output (these
being the 2nd, 3rd , 4th, 5th, 6th and 7th order harmonics!.
Usually, only the first few harmonics are significant, and even-order
harmonics (i.e. 2nd and 4th) are less objectionable than odd-order
harmonics (i.e. 3rd and 5th); higher harmonics may be
negligible in compar ison to the fundamental (100Hz) output.
Therefore, rather than specifying the level of each harmonic com•
ponent, this distortion is usually expressed as T.H.D. or Total
Harmonic Distortion . While T.H.D. is the total power of all
harmonics generated by the circuitry, expressed as a percentage
of the tota l output power, the "mixture" of differe nt harmonics
may vary in different equipment with the same T .H.D. rating.
Harmonics
Overtones which are integral mu ltip les of the fundamental.
Head room
Headroom refers to the "space," usually expressed in dB,
between the nominal operat ing signal level and the maximum signal
level. The inp ut headroom of a circu it that is meant to accept
nominal -10dB levels, but can accept up to +18dB without
overdrive or excessive distortion, is 28dB (from -10 to +18 equals
28dB). Similarly, the output headroom of a circuit that is meant
to supply nomina l +4dB m drive levels, but that can produce
+24dB m before clipping is 20dB. A circuit that lacks adeq uate
headroom is more like ly to distort by clipp ing transient peaks,
since these peaks can be 10 to 20dB above nomina l operating
signal levles.
1.M. (Intermodulation Distortion)
Intermodulation distortion consists of signal components
appear ing at the output of an amplifier or ot her circu it that were
not present in the input signal, that are not harmonically related to
the input, and that are the result of interaction between two or
more inp ut frequencies. 1.M. distortion, like harmonic distortion, is
usually rated as a percentage of the total output power of the
device. While some types of harmonic distortion are musical, and
not particularly objectionab le, most I.M. distortion is unp leasant
to the ear.
Impulse Response
Related to the rise time of a circuit, the impulse response is a
measurement of the ability of a circuit to respond to sharp sounds,
such as percussion instruments or plucked strings. A circuit with
good impulse response would tend to have good transient response.
Level Match
The dbx noise reduction system is unlike competitive systems
in that there is no one threshold at which compression or expansion
begins. Instead, compression occurs linear ly, with respect to
decibels, over the full dynamic range of the program. By necessity,
there is an arbitrary signal level which passesthrough the encoder
and decoder wit hout being changed in level. This level is known as
the level match point (transition point). Some dbx equipment
provides for user adjustment of the level match point, for monitor-
ing purposes only. Although this is not necessary for proper encode/
decode performance, by sett ing the level match point to be approxi -
mately equal to the nominal (average) signal level, there will be no
increase or decrease in level as you switch from monitoring "live"
program to monitoring dbx-processed program.
Limiter
A lim iter is a type of compressor, one with a 10:1 or greater com-
pression ratio. A Iimiter with a high compression ratio (120: 1) can
be set so that no amount of increase in the input signal will be able
to raise the output level beyond a preset value. The difference
between limiting and compression is that compression gently
"shrinks" dynamic range, whereas limiting is a way to place a fixed
" ceil ing" on max imum level, without changing the dynamic range
of program below that "ceiling," or thresho ld.
Line Level (Line Input)
Line level refers to a preamp lified audio signal, in contrast to
mic level, which describes a lower-level audio signal. The actual
signal levels vary. Generally, mic level is nominally -50dBm (with
typical dynamic range of -64dBm to +1OdBm). Line level signals
vary, depending on theaudio system. Hi-Fi line levels are nominally
-15dBV, whereas professional line levels are nomina lly +4dBm or
+8dBm (with typical dy namics ranging from -50dBm to +24dBm).
Line inputs are simply inputs that have sensitivities intended for
line level (preamp li fied) signals. Often, the nominal impedance of a
line level input wil l be different t han the nominal impedance of a
mic level input.
Modul ation Noi se
Modulation noise is a swishing type of background hiss that
occurs with tape recordings in the presence of strong low frequency
signals. The noise depends on the level of the recorded signal; the
higher the recorded signal level, the higher the modulation noise.
Modulation noise has typically been "masked," hidden by the
dominant signal and/or by the background hiss of the tape. How-
ever, when the background hiss is removed, as with dbx processing,
modulation noise could become audible. This would happen
primarily with strong, low-frequency signals, but in fact it is
minimized by dbx 's pre-emphasis and de-emphasis.
reduction systems which depend on peak or average level
detection circuitry.
Octave
In mus ic or audio, an interval between two frequencies having
a ratio of 2: 1.
Overshoot
When a compressor or expander changes its gain in response to
a fast increase or decrease in level, the maximum gain change should
be directly proportional to the actual signal level. However, in some
compressors the level detection and gain changing circuitry develop
a kind of "inertia," over-reacting to changes in level, increas ing or
decreasing the gain more than the fixed ratio asked for . This over-
reaction is known as overshoot, and it can cause audibly non-linear
compression (distortion). dbx circuits have minimal overshoot, so
they provide highly linear compression and expans ion.
Peak Level
An audio signal continuously varies in level (strength, or
maximum voltage) over any period of time, but at any instant, the
level may be higher or lower than the average. The maximum
instantaneous value reached by a signal is its peak level (see
RMS level).
PhaseShift
"Time shift" is anot her way to describe phase shift. Some
circuitry, such as record electronics and heads, wi ll delay some
frequencies of an audio program with respect to other portions of
the same program. In other words, phase shift increases or decreases
the delay time as the frequency incre<1ses.On an absolute basis,
phase shift cannot be heard, but when two signals are compared to
one another, one having a phase shift relative to the other, the
effects can be very noticeab le, and not very desirable. Excessive
phase shift can give a tunnel-like qual ity to the sound. Phase shift
also can degrade the performance of compander type noise
Power Amplifier
A unit that takes a med ium-level signal (e.g., from a pre•
amplif ier) and amp lifies it so it can dr ive a louds peaker. Power
amplifiers can operate into very low impedance loads (4-16 ohms),
whereas preamplifiers operate only into low impedance (600
ohms) or high impedance (5 ,000 ohms or higher) loads. Also
know n as a main amplifier, the power amp lifier may be buil t into
an integrated amp lifi er or a receiver.
Preamplifier
A device whic h takes a small signal (e.g., from a microphone,
record player), or a medium-level signal (e.g., from a tuner or tape
recorder), and amp lifies it or routes it so it can drive a power
ampl ifier. Most preamplifiers incorporate tone and volume con-
tro ls. A preamp may be a separate component, or part of an
int egrated amp lifier or of a receiver.
Pre-Emphasis (See "de-emphasis")
Receiver
A single unit that combines tuner, preamp and power amplifier
sections.
Release Time or Release Rate (See "decay time" and "attack time")
Rise Time (Att ack Time)
Thi s is the ability of a circuit to follow (or "track") a sudden
increase in signal level. The shorter the rise ti me, t he better the
frequency response. Rise time is usually specified as the interval
(in microseconds) required to respond to the leading edge of a
square-wave input.
RMS Level
RMS level (Root Mean Square) is a measurement obtained by
mathematically squaring all the instantaneous voltages along the
waveform, adding the squared values together, and taking the
square root of that number. For simp le sine waves, the RMS value
is approximately 0.707 times the peak value, but for comple x audio
signals, RMS value is more difficu lt to calculate. RMS level is
simi lar to average level, although not ident ical (Average level is a
slower measurement).
VI

VII Sub Harmonic
A sub-mul tiple of the fundamental frequency . For example,
a wave the frequency of which is half the fundamenta l frequency
of another wave is called the second sub harmonic of that wave.
Sub Woofer
A louds peaker made specifically to reproduce the lowest of
audio frequencies, usually between 20Hz and 1OOHz.
Synthesizer
An ELECTRONIC MUSIC SYNTHESIZER is an aud io
processor th at has a built-in sound generator (oscillator), and
that alters the envelope of the sound wit h voltage contro lled
circuitry. Synthesizers can produce familiar sounds and serve as
musical instrume nts, or they can create many uniq ue sounds
and effects of their own.
A SUB HARMONIC SYN T HESIZER is a device whi ch is not
used to create music, but to enhance an existing audio program.
In the case of the dbx Mode l 100 , the unit creates a new signal
that corresponds to the volume of the input signal , but is at
1/2 the freq uency of the inpu t signal.
Tape Saturation
There is a maximum amount of energy that can be recorded on
any given type of magnetic tape. When a recorder "tries" to record
more energy, the signals become distorted, but are not recorded at
any higher levels. This phenomenon is called tape saturation
because the magnet ic oxide particles of the tape are literally
saturated with energy and cannot accept any more magnetization.
T.H.D. (Total Harmonic Distor tion) (See "Harmonic Distortion")
Threshold
Threshold is the level at whic h a compressor or limiter ceasesto
have linear gain, and begins to perform its gain-changing function
(i.e., where the output level no longer rises and fal ls in direct
proportio n to the input level). In most systems, the threshold is a
point above wh ich the level changes, althoug h there are compressors
that raise signal levels below a thresho ld point. Some compander-
type noise reduction systems, such as Do lby ~ * have upper and
lower threshold between which the gain changes; these systems
require carefu l level calibration for proper encode/decode perfor -
mance. dbx noise reduct ion systems have no threshold at which
compression or expansion factors change, so level calibration is
not critica l.
*'Dolby' is a trademark of Dolby ® Laboratories, Inc.
Triamplified
Similar to biamp lified. A sound system where a passive cross-
over network creates three frequency ranges, and feeds three power
amplifiers : one for bass, one for mid, and one for high frequencies .
The amplifiers are connected direct ly to the woofers, midrange
drivers and tweeters w ithout a passive, high-level crossover network .
Tuner
A unit which receives radio broadcas ts and conve rts them
into audio frequency signals. May be part of a receiver .
VCA (Voltage Controlled Amplifi er)
Traditiona lly, amplifiers have been designed to increase signal
levels (to provide gain) . If an amp lif ier were required to decrease
the level (to attenuate), it could become unstable , and might even
oscillate . The gain (amount of amp lification) in these traditiona l
amp Iifiers wou Id be adjusted by one of three methods (1) attenuat-
ing the audio signa l fed to the input of the amplif ier, (2) attenuating
the audio output of the amplifier, or (3) changing the negative feed-
back (feeding more or lesssigna l from the output back to the input,
but in reversed polar ity).
The VCA is a special type of amplifier that can be used to
increase or decrease levels over a wide dynamic range. Instead of
using signal attenuation or negative feedback, the gain (or loss) is
adjusted by means of an external de contro l voltage. dbx has a
unique, patented VCA design that has extreme ly low noise and
very wide dynamic range; the dbx VCA is the heart of dbx noise
reduction equipment.
Woofer
A loudspeaker wh ich reproduces only low frequencies.
INPUT
Tracking Accuracy
--OUT PUT-~
2 1
Comp,cn1ori 120: 1 Comp1eu1on
(hm 111ng)
-Th 1e1hold --- --- - - - ~~ ----
Tracking refers to the abi lity of one circuit to "follow" the
changes of anot her circu it. When two volume controls are adjusted
in exactly the same way, the corresponding "sameness" of the
output levels can be expressed as the tracking accuracy of the
controls.
The level detection circuitry in a dbx encoder sensesthe signal
level, changes the gain, and creates an encoded signal. The corre-
sponding "sameness" of the origina l signal and the encoded/
decoded signal can be exp ressed as the track ing accuracy of the
noise reduction system. (dbx systems are non-critica l for the
operator, and are built to close tolerances, so that tracking
accuracy is exce llent, even if the encoder and decoder are in
different pieces of dbx equipment.)
Transition Level (See Level Match)
When a circuit has uniform compression or expansion through-
out its fu ll dynamic range, there must be some level which passes
through the unit without being raised or lowered (where gain is
unity). This un ity gain level is the transition level or transition point.
The trans ition point is a "window" 1dB wide, in a dbx encoder
(compressor), alI signals above the transition point are decreased in
level, and all signals below the point are increased in level. Con -
versely, in a dbx decoder (expander), all signals above the
transition point are increased in level, and all signals below the
point are decreased in level. The transition level is similar to a
"threshold," except it does not refer to a point at which
compress ion or expansion factors change.
VIIl