Studio Technologies 210 2012 - Manual (Page 26)

Issue 5, September 2012 Model 210 User Guide
Page 26 Studio Technologies, Inc.
interconnecting cables. All Model 210
XLR connectors have a ground connection
that is made to the interfacing connector’s
metal “shell.” And most XLR connectors
have a pin or connection point available
to access its metal shell. By connecting
the cable shield to the mating connector’s
shell terminal, the common connection
typically found on audio interconnections
is created.
IFB Channel Crosstalk
By the very nature of its design, a stan-
dard “wet” IFB circuit is prone to exhibit
cross-talk between its two audio channels.
This occurs because the audio paths are
unbalanced (“single-ended”) and typically
transported on a single shielded twisted-
pair audio cable. The primary cause of
the crosstalk is the capacitance between
the wires in the cable pair. The greater the
capacitance, due to cable type and length,
the more crosstalk there will be. It’s not
surprising to find in sports broadcasting
venues that audio from one channel in
an IFB circuit can be heard “bleeding”
into the other channel. Does this generally
create a problem? No, as each channel
in an IFB circuit generally carries related
audio content. For example, on-air talent
hearing in their left ear a small amount of
program audio from channel 2 while an
interrupt from channel 1 is active, typically
wouldn’t perceive this as an issue.
There are several ways of reducing IFB
channel crosstalk. Probably the easiest
way is to use cable pairs that are not twist-
ed. Twisted pairs are great for differential
(balanced) signals, but not so great for
unbalanced transmission. This is gener-
ally because the more twists in a pair the
greater the effective cable capacitance.
In a stadium or arena setting, choosing
standard “telco” pairs may actually work
better than “high-performance” audio or
data cable!
Another option is to use two cable pairs
for each IFB circuit. If the pairs are not
shielded the wiring is simple. Common
would be connected to one side of each
pair, and then signal from each channel
would connect to the other side of the
pairs. If the pairs also contain shields
the wiring could be done somewhat differ-
ently. One option is to connect common
to both cable shields, IFB channel 1 (DC
with audio) to one full pair, and IFB chan-
nel 2 to the second full pair. A better
option might be to have common connect
to both shields and one side of the pair
that serves IFB channel 2.
Other options are available if an applica-
tion demands low crosstalk. If resources
in the broadcast or production facility
allow one method would be to run the
IFB circuits “dry” (no DC) and differential
(balanced). This would gain the benefits
of differential transmission, including mini-
mizing the crosstalk. If optional line input
cards have been installed in the Model
210, the balanced line-level signals can be
directly connected. However, if it’s desired
to connect cue sources to the Model 210
using an IFB-type circuit, the line-level
audio signals will need to be “wetted up”
into standard IFB circuits. This is easily
accomplished using one of several high-
performance IFB interface units from
Studio Technologies. For further informa-
tion please refer to the Studio Technolo-
gies website.
IFB Audio Levels
The Model 210 is designed to operate
best with IFB audio levels that are nomi-
nally –10 dBu. This is the nominal level