Studio Technologies 72 - Manual (Page 6)

Issue 2, July 2004 Model 72 User Guide
Page 6 Studio Technologies, Inc.
Model 72
Level Meter / Interface
Technical Notes
Channel Assignments
By design, the Model 72 doesn’t define
what signals will be present on the pins
of the connected IFB or intercom circuit.
This is because of the many different ways
signals and signal names can be assigned
to the same type of circuit. For univer-
sality, the meters and audio outputs are
referenced to the pins on the IFB/intercom
input, rather than having assigned names.
This naming method leads to one level
meter and one audio output being asso-
ciated with pin 2. The second meter and
audio output is associated with pin 3. For
reference it may be worthwhile to list some
standard pin assignments:
• In broadcast IFB applications pin 2 is
often defined as the “interrupt” or the
“program-with-interrupt” channel. It
may also be referred to as IFB channel
1. Pin 3 is often defined as “program”
or “program-only.” It may also be re-
ferred to as IFB channel 2.
• Many broadcast applications use
TW-type intercom systems from RTS.
In these cases pin 2 will be intercom
channel 1; pin 3 will be intercom
channel 2.
• Often theatrical and industrial applica-
tions use single-channel intercom sys-
tems from Clear-Com. In these cases
pin 2 will only provide DC power, hav-
ing no audio source associated with
it. Pin 3 will provide intercom audio or
intercom channel 1.
Power LED and Input Voltage
It’s important to note that the LED labeled
PIN 2 POWER will light essentially any
time a positive DC voltage is present on
pin 2 of either of the IFB/intercom input
connectors. Any DC that’s above approxi-
mately 3 volts is sufficient to light the LED.
This is by design as the LED is really just
intended to indicate that a “wet” circuit
has been connected. For full Model 72
operation the DC input needs to be in the
range of 20 to 22 volts.
IFB Audio Levels
The nominal level of audio signals associ-
ated with IFB circuits is typically –10 dBu.
This is the case with the interface units
from Studio Technologies, as well as such
systems as the RTS 4000-series. But actu-
ally having the correct level present
on an IFB circuit is often a “hit-or-miss”
proposition. During field testing Studio
Technologies’ personnel found that a
wide range of nominal audio levels were
present on “real-world” IFB circuits. Many
were fine, being reasonably close to the
desired –10 dBu. But some were much too
low, while others were much too “hot.” We
observed one unfortunate baseball “color”
commentator being sent interrupt audio
signals so “hot” relative to program audio
as to almost make his ears bleed! This
situation should not have been allowed
to happen.
In defense of field technical personnel,
measuring the audio level of an IFB circuit
hasn’t traditionally been an easy proposi-
tion. But that situation has now changed
with the Model 72. Using the unit will allow
level controls on the source equipment to
be adjusted as required.