Studio Technologies IFB Plus 2005 - Manual (Page 17)

Model 2 User Guide Issue 8, December 2005
Studio Technologies, Inc. Page 17
The red LED, labeled IFB, is lit any time pro-
gram audio is being interrupted. There are
three ways an interrupt can take place: by
the internal microphone being activated, 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 pro-
gram audio signal to be adjusted relative to
the interrupt audio level. The interrupt level
is internally fixed and serves as the refer-
ence. 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 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