Studio Technologies 230 2014 - Manual (Page 35)

Model 230 User Guide Issue 9, November 2014
Studio Technologies, Inc. Page 35
talkback outputs’ interconnecting cables.
All Model 230 XLR connectors have a
ground connection that is made to the
interfacing connector’s metal “shell.” And
most XLR connectors have a pin or con-
nection 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 cre-
ate 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 different-
ly. One option is to connect common
to both cable shields, IFB channel 1
(DC with audio) to one full pair, and IFB
channel 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 al-
low 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. The balanced line-
level signals can be directly connected to
the Model 230’s line inputs. However, if
it’s desired to connect cue sources to the
Model 230 using an IFB circuit, the line-
level audio signals will need to be “wet-
ted 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.
The discussion in the previous paragraphs
concerning IFB circuits can also apply to
single- and dual-channel intercom lines.
The same type of cabling is typically used
for both, resulting in the same crosstalk
issues. However, by their very nature as