OPERATION
8e
APPLICATIONS
Additional Information on the Setting and
Function of Certain Controls.
Compression Control
This control is continuously
adjustable from a com-
pression ratio of 1 M to infinite compression (that is,
no
change in output
level
regardless of changes in input
level above the set threshold). High compression (settings
greater than 6) significantly level out program materials.
Infinite compression virtually
stops music levels from
exceeding the threshold setting. Lower compression
settings (below
4)
still permit
dynamic range to exist.
They are used
to
tighten up the
sound of a bass guitar,
lead
guitar, snare drum, kick drum and vocals. Moderate
overall compression is typically
used
during
stereo
mixdowns. Here a variety of settings could
be
used.
While any compression ratio can be set with this
control,
remember that the Over Easy curve causes
that ratio to be approached gradually
as
the input
signal
level
rises through the threshold. Only when the
input signal
is
considerably
above the threshold does the
165 closely approach the
set
ratio of compression.
(See
Figure
3.)
Threshold Adjustment & LED Indicators
The
Threshold control sets the level at which the 165
begins
to
compress the signal
(i.e., it sets the point
where the Over
Easy compression curve
intersects
the
input signal). The control has
a
wide range
so
that
the
desired
results
can be obtained with any line level input
signal. When the Threshold
control is set too low, the
165 will compress most
if not
all
of the input signal
(red LED ON most of the time). At low
compression
ratios, the very low threshold setting can be used
to
gently
reduce
the
overall dynamic range of the program.
Low threshold settings (—20
to -40) are used when
program materials are
to
be compressed.
Low
settings,
with high
input
levels,
cause the 165 to "'work" all
or
more of the
time
than with lower input
levels.
The
major portion of program material is processed with
a
low threshold setting, Normal compression
and "leveling"
of vocals and instruments typically
use
lower
settings.
Compression of the whole program, however, may not
sound natural, especially
at
compression ratios
of
10:1
or greater. High threshold
settings
(—10
to +10) are
used for limiting program levels
or
where
only peaks are
to be compressed. The major portion of the program
material is not processed
with a
high
threshold setting.
Speaker protection and peak overload prevention are
just two applications.
NOTE: Whenever threshold
level and compression ratio
settings
are made, it is important to watch the LED's
and meter for reference
andconfirmation. Remember
that a compressor/iimiter is
a
tool that can provide
desirable effects when
used properly. When used
to
excess, the results
can sound unusual, and may be of
value only for special
effects.
With the Compression
control set for the desired
maximum compression ratio
(or an approximation
thereof), rotate the Threshold control
counterclockwise
until the desired sound, special effect, or amount of
gain
reduction is
achieved.
Auto Switch & Auto Attack/Release LED Indicator
When the
Auto
switch is
IN (Auto Mode), the LED
indicator will be iliuminated and the Model
165
will
automatically adjust its
attack rate and release time to
suit the program envelope. (This Auto Model
sets
the
Model
165 for
the
same attack and release characteristics
as dbx Models
160, 161, 162,
163 and 164 compressor/
limiters.) When the Auto
switch is OUT (manual mode),
the LED indicator above it turns OFF,
and the front
panel
Attack
and
Release
rate controls determine the
maximum rate of gain change
and
the
behavior of the
level
detector circuitry (see below).
Attack
Rate
&
Release Rate
Controls
The Model 165 is the first dbx compressor/limiter
to
offer a choice of automatic or user adjustable
attack and
release characteristics. In
Auto
Mode,
the 165 utilizes
the
patented dbx RMS level detector with its program
dependent attack/release
characteristics to obtain
natural-sounding compression
or limiting.
For
special
effects and certain signal situations, however, it is
often
desirable
to set
fixed
attack and release characteristics.
Manual mode affords this capability.
The Auto
Mode
is
recommended for vocals
as
well
as
instruments. When
determining
separate attack and
release
rate control
settings, it provides
a
good starting point. Because the
Auto Mode has a variable attack rate, the 1
65
may
compress or limit some program materials smoother
than in the manual mode which
has a fixed rate of
attack. This is especially true
on
vocals.
Where To Set Attack 8c Release Controls
There is
no
"right"
way to set the Attack and
Release controls. Generally,
one would want a slow
enough Release
to
avoid "pumping"
or
"breathing"
sounds caused when background sounds are audibly
modulated
by
the dominant
signal energy, yet the
release must
be
fast enough
to avoid suppression of the
desired signal after
a
sudden
transient or a loud note has
decayed.
Depending
on the desired effect, one might
want
a
very slow Attack
so
that
percussive or transient
sounds are not restricted, but average volume levels
are
held
within
the
desired range.
A very fast attack setting (control maximum
counter-
clockwise) will
cause the 165
to
act like
a
peak limiter
even though RMS detection
circuitry is used. Slower
attack settings cause the 165 to act like an RMS or
averaging detecting compressor/limiter.
Don't forget,
attack and release controls operate together
and with
the compression
ratio control. Changing any one control
may necessitate changing the other settings.
Meter
Calibration & Use
The meter In the
165
is factory
calibrated to
indicate
"0"
when the signal level is +4 dB
(1.23 V)
at
either
the input
or
output of the 1
65,
depending
on the meter function switch
position. (When the
meter
is
in Gain Change
mode,
"0"
indicates no gain
change; the meter calibration
control does not affect
this mode.)
To recalibrate the meter, engage the Input meter
function switch and feed
a 1
kHz
signal at the selected
nominal operating level (the level desired
for a
"0
VU"
meter indication) to the
165's
signal
input.
Then
adjust
the
rear
panel METER
CALIBRATION control until the
meter indicates
"0
dB".
Use of an Equalizer in the Level Detector
Circuit for
Frequency
Weighted Compression, De*esslng, or
Increasing
Sustain
It
is
possible
to "separate" certain instruments from
a
mix
by
frequency
weighted compression. This function
is created
by
inserting
an
equalizer
ahead of the Model
165's level detector input, but not in the main
signal
input path.
Peaking
the equalizer in
a
certain
frequency
range
will tend to suppress any frequencies (notes) in
that register. A relatively high
threshold setting can
allow normal sounds to be unaffected while
solo or very
8
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