Operation Manual

T
ROUBLESHOOTING
ASPI Digital - The Sound of DSP Technical Support: 404.892.3200 47
reduces the ability of the decision logic to determine whether the AEC should be in
transmit, receive, or double-talk mode. This effect may reduce the effectiveness of
the EF1210 in canceling echoes.
You can check for insufficient microphone amplification by observing the front panel
I
NPUT
L
EVEL
I
NDICATOR
during normal conferencing conversation. The first yellow
LED should illuminate frequently. If the I
NPUT
L
EVEL
I
NDICATOR
never illuminates
beyond one or two green LEDs during normal speech, increase the microphone’s
input level.
Loudspeaker
Nonlinearity
Overdriving the loudspeaker may distort the zone output signal and cause ineffective
AEC operation. The EF1210 relies on the linearity of the acoustic feedback path —
D-A, amplifier, loudspeaker, microphone, and A-D — to cancel acoustic echoes. If
you overdrive the loudspeaker, the acoustic reflections picked up by the microphone
do not match the signal fed to the loudspeaker. They are distorted copies of this sig-
nal. The EF1210 cannot effectively cancel this distorted signal.
If you suspect the loudspeaker is introducing nonlinearities into the room acoustic
path, take these steps to minimize its influence on the echo canceller.
• Keep the loudspeaker’s volume level at less than three-eighths of full scale. If
higher volume is required, the EF1210 should operate effectively at volume set-
tings of up to 50 percent of full scale. At more than 50 percent, most audio sys-
tems and loudspeakers introduce significant nonlinearities. The EF1210 may not
adapt under these conditions, and echoes may be heard.
• If the loudspeaker has a bass control, lower it. Excessive bass can cause a boomy
effect that is nonlinear. In addition, excessive bass may cause substantial
mechanical coupling to the microphone through vibrations induced in the hous-
ings and support structures.
• Increase the separation distance between microphones and the loudspeaker. The
EF1210 handles up to 10 dB of acoustic gain between the loudspeaker and the
microphone. You may be exceeding this limit if the loudspeaker is pointed
directly at the microphones or if the loudspeaker volume is excessive (loud-
speaker placement is not critical, but it should not be pointed directly at the
microphones).
R
EMOTE
C
ONTROL
P
ROBLEMS
If the remote control device doesn’t seem to be affecting the EF1210, there are a few
things you can check. Try sending commands that have a visible impact, like the
MUTEI command (muting all channels will cause the M
UTE
A
LL
LED to light). Also,
look for messages from the EF1210, like acknowledgment or error messages, if the
remote control device can display them.
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.