Studio Technologies IFB Plus 2007 - Manual (Page 20)

Issue 9, January 2006 Model 2 User Guide
Page 20 Studio Technologies, Inc.
of rotation (12 o’clock) will give a program
level approximately equal to the interrupt
level. This statement is made under the as-
sumption that a +4 dBu program 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 (program 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 “head-
room” 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 maintenance,
as well as during normal operation.
A typical interrupt signal will light the green
LEDs, with peaks lighting the yellow LED.
The internal compressor circuits 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 function
that allows an audio signal to automatically
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 di-
rector 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
program audio and routing VOX audio in its
place. The VOX interrupt can be assigned
to either IFB channel 1 or 2, but not to both
simultaneously.
The VOX interrupt function is only sophisti-
cated from an internal-circuitry stand point.
Operation is quite simple, with only two
switches to set. The input switch allows one
of three audio sources to be connected to
the VOX input: audio from the auxiliary audio
input, receive audio from telephone interface
1, or receive audio from telephone inter-
face 2. The output switch is used to select
whether the VOX interrupt function is off (not
used), or is assigned to interrupt IFB chan-
nel 1 or 2. VOX operation can commence
as soon as the output is assigned to one of
the channels. VOX interrupt activity can be
noted by observing the yellow VOX LED as-
sociated with the assigned IFB channel.
Telephone Interface 1
Two status LEDs, one switch, and one trim
potentiometer are associated with telephone
interface 1. The yellow LED, labeled STD, is
lit whenever the interface is set for the stan-
dard audio mode by the switch on the back
panel. The red LED, labeled LC for loop
current, lights any time DC current is flow-
ing through the interface. Normally in the
standard audio mode, loop current would
not be flowing through the interface and
the LC LED will not be lit. In most cases the
loop current LED lighting would indicate that
the mode switch should be changed to the
telephone line position.
The interface control switch, active in the
telephone line mode, allows the interface to
be taken off hook or hung up. Momentarily
pressing the switch to the up position, la-
beled MAN OH for manual off hook, places