Studio Technologies IFB Plus 2001 - Manual (Page 20)

Issue 7, November 2001 Model 2 User Guide
Page 20 Studio Technologies, Inc.
sound enters the microphone via the
small openings in the front panel above
and slightly to the right of the switches.
Program Select, Level Adjustment, and
Indicators
Two identical sets of controls and indica-
tors serve IFB channels 1 and 2. Each
channel contains six program select
switches, two status LEDs, a program
level control, and a 5-segment LED level
meter. The six switches are used to select
which of the four program inputs, and the
receive audio from the two telephone
interfaces, will serve as the program audio
source(s). The switches were chosen to
allow more than one source to be selected
at a time. The ability to simultaneously
depress and lock multiple buttons is not
a defect, but is a feature which can be
useful in special circumstances.
The red LED, labeled IFB, is lit any time
program audio is being interrupted. There
are three ways an interrupt can take place:
by the internal microphone being acti-
vated, by a Model 22 Access Station being
used, or via a control signal from the voice
operated (VOX) interrupt function. The
yellow LED, labeled VOX, is lit any time
interrupt is caused by the VOX function.
The program level control allows the
program audio signal to be adjusted
relative to the interrupt audio level. The
interrupt level is internally fixed and serves
as the reference. The gain structure was
configured so that the level control set for
50 percent of rotation (12 o’clock) will give
a program level approximately equal to
the interrupt level. This statement is made
under the assumption that a +4dBu pro-
gram signal is selected and its associated
input trim pot is correctly set.
The 5-segment LED level meter displays
the internal level of the composite (pro-
gram and interrupt) IFB signal. The three
green LEDs are lit with signals in the
normal operating range. The yellow LED
lights with a signal slightly higher than
average. The red LED lights when signal
levels are in the “headroom” area. The
ballistics of the meter are a cross between
that of a VU meter and a peak (PPM)
meter. (We affectionately refer to it as
a “PU” meter!) The meter should prove
useful during installation and mainte-
nance, as well as during normal operation.
A typical interrupt signal will light the
green LEDs, with peaks lighting the yellow
LED. The internal compressor/limiter will
keep most interrupt signals from lighting
the red LED. When an interrupt is not
taking place, the level meter will reflect the
level of the program audio source. Setting
the program level control to occasionally
light the yellow LED will give a program
level approximately equal to the interrupt
level.
Voice Operated (VOX) Interrupt
The Model 2 contains a specialized func-
tion that allows an audio signal to auto-
matically interrupt the program signal.
By contrast, using the Model 2’s internal
microphone requires an explicit action
by the operator, i.e., pressing a button
to cause an interrupt. In some cases, this
explicit action is simply not possible. An
example would be a director giving cues
via a two-way radio or a telephone line.
The VOX circuitry creates an interrupt
control signal by detecting energy in the
voice band. This control signal acts on the
selected IFB channel, interrupting pro-
gram audio and routing VOX audio in its
place. The VOX interrupt can be assigned