Polycom EF2241 manual Insufficient, Nonlinearity

TROUBLESHOOTING

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 LEVEL INDICATOR 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.

Note. Before you readjust the microphone input levels, check to

		make sure you are looking at the correct channel on the LEVEL
		INDICATOR.
		Note. If you adjust the MIC/LINE INPUT level, you will affect the
		room gain. Check to make sure that the room gain limit is not
		exceeded. See “Verify Room Gain” on page 14.
Insufficient
	Grossly insufficient microphone gain degrades EF2241 performance and weakens the
Microphone	out-bound speech power level. This has the effect of reducing the signal-to-noise
Amplification	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
	LEVEL INDICATOR during normal conferencing conversation. The first yellow LED
	should illuminate frequently. If the LEVEL INDICATOR never illuminates beyond one
	or two green LEDs during normal speech, increase the microphone’s input level.
		Note. Before you readjust the microphone input levels, check to
		make sure you are looking at the correct channel on the LEVEL
		INDICATOR.
		Note. If you adjust the MIC/LINE INPUT level, you will affect the
		room gain. Check to make sure that the room gain limit is not
		exceeded. See “Room Gain” on page 39.
Nonlinearity
	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.

VORTEX EF2241 Reference Manual 42 Technical Support: 800.932.2774