Studio Technologies 42A 2008 - Manual (Page 15)

Model 42A User Guide Issue 2, February 2008
Studio Technologies, Inc. Page 15
Audio Monitoring
The dual 5-segment LED level meters
allow a direct observation of the audio
levels present on pins 2 and 3 of the se-
lected IFB circuit’s output connector pair.
In television broadcast settings, the left
meter will typically display the “interrupt”
signal while the right meter will display
“program.” A quick glance at the meters
will give an accurate overall indication of
a circuit’s performance. During the initial
power-up period, lasting approximately
ten seconds, the meters may be observed
“bouncing” if the IFB circuit selected for
monitoring is changed. This is normal,
caused by DC blocking capacitors taking
a minute or two to reach their final state.
It’s important to note that the meters on
the Model 42A are calibrated differently
from the typical “VU” scale. The level
steps were selected so as to effectively
display the IFB circuit’s nominal –10 dBu
signal level. The ballistics of the meters
is also different, being a cross between
VU and peak. The bottom four LEDs are
green in color and indicate that signals
are in the normal range. The top LED,
yellow in color, lights when signals are
6 dB or greater above –10 dBu. A correctly
functioning IFB circuit should find signals
lighting the four green LEDs, with the
yellow LED lighting only on peaks.
The headphone output allows audible
monitoring of the selected IFB circuit.
The 2-channel (stereo) output is compat-
ible with virtually any pair of stereo head-
phones. As the output circuitry meets
“pro audio” specifications, it’s recom-
mended that high-quality headphones be
used. Pin 2 of the selected IFB circuit is
the signal source for the left channel of the
headphone output. Pin 3 of the IFB circuit
is the source for the right channel. The
rotary control adjusts the output level of
both the left and right channels. Should it
be necessary, there’s no reason why the
headphone output couldn’t also be used
as a line-level monitor output.
The front-panel-located pushbutton switch
serves two purposes: selecting the IFB cir-
cuit to be monitored and enabling the auto
scan feature. To manually select an IFB
circuit to be monitored, press and release
the button until the status LED associated
with the desired IFB circuit lights. Each
press of the button will advance the circuit
number to be monitored by one. A delay
is built into the circuit selection process
Figure 9. Detail of front panel showing
headphone section Figure 8. Detail of front panel showing dual
5-segment LED level meters