Studio Technologies 210 2008 - Manual (Page 25)

Model 210 User Guide Issue 4, October 2008
Studio Technologies, Inc. Page 25
Technical Notes
Grounding and Shielding
As previously discussed in this user guide,
the pin 1 connections on both the main
and talkback outputs’ 3-pin male XLR-type
connectors are “floating,” i.e., not con-
nected to anything within the Model 210’s
enclosure. Some audio experts might take
offense to this, grousing that this should
have been left to the user or installer to
be connected or disconnect as desired.
However, repeated field testing found that
floating pin 1 on the outputs was the key
to maintaining quiet audio. From Fenway
Park, to the Orange Bowl, and then north-
west to Husker Stadium, lifting pin 1 did
the trick.
A simple solution is available if an
application does require that a ground
be available on the main and talkback
outputs’ interconnecting cables. All Model
210 XLR-type connectors have a ground
connection that is made to the interfacing
connector’s metal “shell.” And most
XLR-type 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
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 op-
tion 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