Studio Technologies 42A 2008 - Manual (Page 6)

Issue 1, February 2008 Model 42A User Guide
Page 6 Studio Technologies, Inc.
typically in the range of 30 to 32 volts.
The audio is unbalanced with a typical
nominal level of –10 dBu. The Model 42A
implements wet IFB circuits. As such, in
this user guide the term IFB will always
represent this type of circuit.
IFB circuits provide an effective means
of delivering power and two channels of
audio to user devices by means of stan-
dard audio cables. These cables, ubiqui-
tous to the audio industry, interface using
3-pin male and female XLR-type connec-
tors. Using IFB circuits and standard audio
cables it’s a simple matter to support user
devices such as listen-only belt packs and
announcer’s consoles with no external
power source required. Whether the IFB
source and user devices are 100 or 1000
feet apart, reliable operation can almost
always be provided.
In many cases, the Model 42A Interface
will be used in on-air television applica-
tions. Whether installed in a fixed location
or as part of a remote facility, the unit is
capable of providing excellent perfor-
mance. In addition, the Model 42A is ap-
plicable for non-broadcast applications.
For example, audio recording and post-
production facilities can also effectively
use the Model 42A. Combined with stereo
or mono listen-only belt packs, also avail-
able from Studio Technologies, a variety
of headphone cue systems can easily
be deployed. And since the Model 42A’s
audio inputs are compatible with standard
line-level audio signals virtually any analog
source can be connected.
Four Independent IFB Circuits
The Model 42A supplies four independent
IFB circuits. Each circuit consists of two
audio inputs and a 2-channel “wet” IFB
output. The audio inputs are transformer
coupled, have a nominal level of +4 dBu,
and are compatible with balanced or unbal-
anced sources. In on-air television broad-
cast applications the audio sources will
often be analog outputs from matrix inter-
com systems. Two sources are typically
designated to serve as user cue signals.
Generally one source is configured in the
matrix intercom system as “interrupt” while
the other is configured as “program.” An
alternate term often used for the “inter-
rupt” channel is “program-with-interrupt.”
This may be more descriptive as the func-
tion is actually a program source that
gets interrupted with talkback audio. The
“program” channel is typically a continu-
ous source of program audio. An alternate
term is “program-only.” For other applica-
tions, the Model 42A’s audio inputs can
be connected to a 2-channel or stereo
audio source. This configuration may prove
useful in radio broadcasting, audio-with-
picture, or recording studio applications.
The specific application will dictate whether
both cue signals will be utilized by the end
user. In on-air sports broadcast situations
a “double-muff” (stereo) headset will pro-
vide a user with both audio channels, one
for each ear. In interview or news-gathering
applications it’s common to use a single
“earpiece” to provide a user with program-
with-interrupt audio.
Maintaining excellent audio performance
was a major Model 42A design goal—the
hiss, hum, and noise associated with typi-
cal IFB circuits was simply not acceptable.
The Model 42A meets those requirements
with audio that is “on-air” quality: low
distortion, high signal-to-noise ratio, and
ample headroom. On-air talent and guests,
production personnel, and technicians will
all appreciate the clean, quiet cue signal.