Polycom EF2280 Reference Manual page 2

the transmission of VGA signals from laptops
over Cat5.
"Normally we would have used 5-conductor
coaxial cables and run two of them, but at almost
a half-inch in diameter they would have been too
bulky to run through the cable molding we
installed across the floor," Neal says. "But the
CatLinc allowed us to take VGA connectors to
each of the table pockets and run them back to
an Extron SW4 VGA Ars [audio] switcher situ-
ated under the conference table."
To simplify the system' s operation, Neal used
the switcher on auto switch mode to enable
VGA signals, regardless of source, to be selected
and transmitted to the projector. However, the
computer audio and video signal from the Epson
ELP-DC02 document camera also needed to be
addressed. Neal used a pair of Intelix V2A2 balun
devices to solve the problem.
"The balun device gets two video and two
audio signals across a single Cat5 cable with no
degradation or hum induction," he says.
Knepp says the finished product has been a
success. After the nearly $40,000 project that
spanned roughly a week earlier this year was
completed, Adventist Health has ramped up its
use of videoconferencing, with the ability to
spend more time on the content of its collabora-
tive meetings, rather than on technical setup.
"Between the videoconferencing, voiceconfer-
encing, and use of WebEx, we've been able to cut
down significantly on travel and the quality of
our conferencing has improved," Knepp says.
"The technology to be able to do this has
improved and its cost has come down. More
importantly, the user interface has reduced the
amount of technological expertise required."
DEALING WITH
POOR ACOUSTICS
It's a reality all AV integrators face. Until AV is considered in the
design phase of every project, more often than not integrators are
adapting less than ideal spaces for AV systems. In fact, a major role
that AV technology performs is to help us optimize rooms with poor
acoustics or sightlines. As video- and voiceconferencing becomes
more popular (and in some cases, essential) manufacturers such as
Polycom have gone to great lengths to address environmental
deficiencies through the use of technologies such as acoustic echo
cancellation.
Installed at the near (or local) end, an acoustic echo canceller
(AEC) prevents the echo of the remote person's voice from being
returned (echoed) to them through the audio system.
Near end
Near speech
AEC
XMT
Nonlinear
+
Processing
-
Echo
Echoes
Distortion
Cancelling
Filter
RCV
Speaker
Far speech
How does an acoustic noise canceller work? At the near end,
echoes of the far speech enter the microphone along with the near
speech. The AEC filters out the echoes through an echo cancellation
filter and nonlinear processing.
Reverberation vs. acoustic echo
Reverberation and echo are not the same thing; however, they are
both caused by sound reflecting from surfaces in a room. Do not
confuse the residual echo of remote speech with the reverberation of
local speech. Reverberation of local speech is caused when the
speech signal arrives at the microphone via several paths (the direct
path and multiple reflections from surfaces in the room). While
reverberation can be unpleasant and can affect speech intelligibility,
it's not compensated for by the AEC, which only removes reflections
of remote speech. If the remote end complains that they hear echo,
ensure they are referring to hearing an echo of their own voice and
not room reverberation of local talkers.
You can't remove the effects of reverberation by changing the
settings of an AEC, but you can minimize reverberation by moving
microphones closer to talkers. A more effective solution is adding
acoustical treatment to the room.
Reprinted with permission from Pro AV
Vortex/VSX 8000
Far end
Near speech +
echoes +
distortion
Far speech
AEC
Reverberation
Acoustic echo
The Polycom
bundle.
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to easy street.
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proavmagazine.com MAY 2004
23