Advanced Use
TANDBERG Director Videoconferencing System
67
Automatic Gain Control (AGC) Settings
Select
‘On’
to allow automatic adjustments (Automatic Gain Control) of audio levels. When
‘On’
,
the AGC maintains the audio signal level at a fixed value by attenuating strong signals and
amplifying weak signals. Very weak signals, i.e. noise alone, will not be amplified.
E
XAMPLE
:
I
N
MOST
CONFERENCES
,
THE
PARTICIPANTS
WILL
SPEAK
AT
DIFFERENT
LEVELS
,
AND
BE
AT
DIFFERENT
DISTANCES
FROM
THE
MICROPHONES
. A
S
A
RESULT
,
SOME
OF
THE
PARTICIPANTS
WOULD
BE
HARDER
TO
HEAR
THAN
OTHERS
. T
HE
AGC
CORRECTS
THIS
PROBLEM
BY
AUTOMATICALLY
INCREASING
THE
MICROPHONE
LEVELS
WHEN
“
QUIET
”
OR
“
DISTANT
”
PEOPLE
SPEAK
,
AND
BY
DECREASING
THE
MICROPHONE
LEVELS
WHEN
“
LOUDER
”
PEOPLE
SPEAK
.
When applying a weak signal in the presence of strong background noise, the leveller might
amplify the background noise as well as the signal. Therefore, in noisy environments, it is advisable
to turn the leveller off.
Tips for improving the echo canceller performance:
•
Place all microphones as far as possible from the loudspeaker. Minimum loudspeaker-
microphone distance should be 1 meter.
•
Place all microphones as close as possible to the persons speaking. By using several
microphones, the ratio distance loudspeaker-to-mic/mic-to-speaker can be increased.
Increasing this ratio improves the echo canceller performance. Avoid distances above two
meters from any participant to his/her closest microphone. If necessary, use several
microphones. Also avoid placing microphones less than one meter from any person.
•
Place all microphones as far as possible from noise sources.
•
Reduce the volume setting. Ensure that the loudspeaker does not distort the audio.
•
The echo canceller tries to estimate the echo path from the speaker system to the
microphones. Moving objects change this path, therefore try to avoid moving objects. Be
especially aware of large objects and objects placed close to either the microphone or the
speaker system as these objects will cause severe changes to the echo path.
•
Avoid putting paper sheets etc. on the microphone.
•
Avoid moving the microphone or loudspeaker.
•
In the event of poor echo cancelling, allow the canceller to adapt. After each change, the
echo canceller requires a few seconds to adapt. Do not change the settings without allowing
the echo canceller to adapt to the new audio environment.
•
In the presence of low frequency noise, enable the noise reduction (NR).
N O T E
T
O
ENSURE
CORRECT
BEHAVIOR
OF
THE
AGC,
IT
IS
CRUCIAL
THAT
THE
LEVELS
ON
THE
INPUT
CONNECTORS
ARE
ADJUSTED
CORRECTLY
USING
THE
AUDIO
INPUT
LEVEL
SETTINGS
. T
HE
AGC
WILL
NOT
COMPENSATE
FOR
SEVERE
MISADJUSTMENT
OF
INPUT
LEVELS
.
