Polycom EF2241 用户手册

T

ROUBLESHOOTING

V

ORTEX

 EF2241

 

Reference Manual

42

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Nonlinear distortion causes a degradation or divergence of the AEC’s internal model 
of the room acoustics.  In this situation, the EF2241 cannot effectively cancel room 
echoes and a substantial amount of echo may be heard by the remote party.

Excessive microphone amplification also increases room gain (See “Excessive Room 
Gain” on page 40.).  You can check for excessive microphone amplification by 
observing the front panel L

EVEL

 I

NDICATOR

 during a normal conference.  The first 

yellow LED should illuminate frequently.  If the second yellow LED is illuminated 
constantly during normal speech or if the red LED illuminates or even flickers, reduce 
the microphone input level.

Grossly insufficient microphone gain degrades EF2241 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 EF2241’s ability to adapt and cancel echoes will be less than optimal.

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 
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 EF2241 in canceling echoes.

You can check for insufficient microphone amplification by observing the front panel 
L

EVEL

 I

NDICATOR

 during normal conferencing conversation.  The first yellow LED 

should illuminate frequently.  If the L

EVEL

 I

NDICATOR

 never illuminates beyond one 

or two green LEDs during normal speech, increase the microphone’s input level.

Overdriving the loudspeaker or inserting a dynamics processor before the EF2241 
may distort the signal that the microphones see causing ineffective AEC operation.  
The EF2241 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 or insert a dynamics processor before the echo canceller, the acoustic 
reflections picked up by the microphone do not match the signal fed to the loud-
speaker.  They are distorted copies of this signal.  The EF2241 cannot effectively can-
cel this distorted signal.