Operation Manual

EF1210 U
SER
M
ANUAL
46 http://www.aspi.com Copyright © 1999, All Rights Reserved
M
ETER
, this indicates a possible problem with the acoustic gain on that microphone
channel.
If this excessive coupling activity level is evident on only one microphone input chan-
nel, that microphone channel should either be redirected to reduce coupling to loud-
speaker audio, or recalibrated as it will need to be turned down. If the excessive
coupling activity is observed on all (or most) microphone channels, then this indicates
either that the room audio is too loud or the reference signal may need to be recali-
brated (this will be indicated by observing low activity levels on the R
EMOTE
S
IGNAL
L
EVEL
M
ETER
).
Excessive
Microphone
Amplification
For the EF1210 to adapt effectively, saturation (overload or clipping) must not occur
at the A-D converter supplying the microphone input. Saturation introduces nonlin-
ear signal distortions into what the AEC expects is a linearly echoed version of the
remote speech.
Nonlinear distortion causes a degradation or divergence of the AEC’s internal model
of the room acoustics. In this situation, the EF1210 cannot effectively cancel room
echoes and a substantial amount of echo may be heard by the remote party.
Excessive microphone amplification also increases acoustic gain (See “Acoustic Gain
Failure” on page 45.). You can check for excessive microphone amplification by
observing the front panel I
NPUT
L
EVEL
I
NDICATOR
during a normal conference. The
first yellow LED should illuminate frequently. If the second yellow LED is illumi-
nated constantly during normal speech or if the red LED illuminates or even flickers,
reduce the microphone input level.
Insufficient
Microphone
Amplification
Grossly insufficient microphone gain degrades EF1210 performance and weakens the
out-bound speech power level. This has the effect of reducing the signal-to-noise
ratio of the microphone signal, which is analogous to raising the background noise
level in the room. Because this noise is uncorrelated with the echoes within the room,
the EF1210’s ability to adapt and cancel echoes is compromised.
A second effect of insufficient microphone gain is that the power of the microphone
input signal may be substantially lower than that of the remote input signal. This
Note.
Before you readjust the Remote input levels, check to make sure
you are looking at the correct remote input level (AEC A or AEC
B) on the R
EMOTE
L
EVEL
I
NDICATOR
. Check to make sure that the
microphone that you are looking at is in the zone that you think it
is in and that you are looking at the correct channel on the I
NPUT
L
EVEL
I
NDICATOR
.
Note.
Before you readjust the microphone input levels, check to make
sure you are looking at the correct channel on the I
NPUT
L
EVEL
I
NDICATOR
. Check also to make sure that you are looking at the
correct corresponding reference input level on the R
EMOTE
L
EVEL
I
NDICATOR
.
Note.
If you adjust the M
IC
/L
INE
I
NPUT
level, you will affect the acoustic
gain. Check to make sure that the acoustic gain limit is not
exceeded. See “Check Acoustic Gain” on page 31.