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The
graph also indicates
the region of the
Threshold
»
Signals
at levels
below the threshold will
not be affected by the compres-
sion/limiting action.
Higher signal
levels
will cause
a
controlled
decrease
in
amplifier gain resulting in
a
change of
dyncimic
range.
The
1178
Input Level control adjusts the
eimount
of signal to be
processed above the threshold, and hence the degree of compression
or limiting
.
The Attack Time of the 1178
is
the time it takes for the
device
to respond to
a
signal which exceeds the threshold.
It
is
variable, and since the adjustment may have
a
significant effect
on
the sound
quality of the program material,
a
more detailed
description
is
given
in the
section
on application.
The Release Time may be defined
as the
time for the limiter
to return to
its
normal gain, after the signal which caused the
gain reduction has dropped below threshold.
The release time
is
variable
and
can also alter the sound of the program material
considerably.
The adjustments are discussed in more detail in
the section on application.
3.2
INITIAL SET-UP
After the Model 1178 has been installed and
is
connected to
both
the signal
source
and the
succeeding equipment according to
Section
II,
power may be turned
ON.
Set the controls
as
follows:
Input
Output
Attack
Release
Compression Ratio
Meter Function
Peak/Avg
CCW
Half rotation
Fully
CCW,
switch
to
OFF position
Half rotation
8:1
+4
dB
Avg
3
.
3
PERFORMANCE CHECK
The following steps will verify the general performance
of the
limiter
and
indicate the operation
of all functions.
If
the unit
fails to pass these tests,
malfunction
is
indicated.
Unless other-
wise indicated, these tests should be performed
for
both channels.
3.3.1
INPUT-OUTPUT SIGNAL LEVEL
Apply
a
sine wave signal with
a
level of
approximately
0
dB
(0.775
V
rms) to the
input terminal.
Turn the Input control CW
to
approximately half-rotation.
There should be an indication on
the VU meter.
Adjust the Output control until the VU meter
reads
"0".
Measured with an external meter, the output signal will
read about +4 dBm.
Push the +8 dB meter function switch.
The VU
indication will drop
by
4
dB.
The actual output level will not
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11 -
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