Polycom EF2241 manual Insufficient, Nonlinearity

Page 44

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

Page 43 Page 45
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Page 43 Page 45
Contents Vortex EF2241 Reference Manual Page Introduction Welcome How to Use This Manual IntroductionProduct Product FeaturesProduct Registration Inputs Outputs Remote Control PRE-INSTALLATION Tools Needed for InstallationWhat’s Included What’s Not IncludedEF2241 Front and Rear Panels PRE-INSTALLATION Installation Connecting the EF2241 to Other EquipmentMounting the EF2241 North American RequirementTypical EF2241 Connections CodecConnecting Multiple Vortex Devices Device IDS on the EF BUSFactory Default Settings Preset Terminating the EF2241Off Check Surrounding Equipment Presets Multiple Vortex DevicesPick a Standard Signal Level Configure Program Audio Sources Calibration Input SettingsIntegrating the EF2241 Into Your System Set Levels on Line Input Channels SET UP the Phone Interface Build Your Echo Canceller ReferenceEcho Canceller Reference for Multiple Vortex Devices Customize Setting for Your Particular ApplicationSetting up Bus ReferenceConfigure the Automatic Microphone Mixer Automixer ParametersGlobal Settings Automixer Settings for Multiple Vortex Devices Channel SettingsBuilding Your System with Multiple Vortex Devices Configure the Matrix MixerDefault Settings Configure the submatrix Assign Inputs Assign OutputsEF BUS Configure Your Echo Canceller Reference PresetsOther EF2241 Features LCD Menu Structure LCD Menu TreeLCD Menu Structure System Menu SystemPhone Control Phone ControlInputs Inputs 1-4, T, A-DOutputs Automixer MenuGlobal Settings Mixer Settings Matrix Menu MatrixParametric EQ Menu Input/Output EQ Channel BandPresets MacrosTroubleshooting Automatic Microphone MixerNo microphones are gating Some microphones are not gating Too many microphones are gatingEcho Canceller Reference Matrix MixerResidual Echo Room Audio Sounds ChoppyFinding the Source of Echo Room Gain Excessive Room Gain Room GainIn-Conference Quick Check Excessive Microphone Amplification Insufficient NonlinearityContacting Technical Support Email vortex@polycom.comTechnical Specifications US Telco requirements ComplianceUSA and Canada Automatic Dialing Telco Connector Canadian Telco RequirementsAustralia Rest of WorldThis page was intentionally left blank CE Mark R& TTE Directive Vortex EF2241 Reference Manual Technical Support Conference System Design Noise and Reverberation Consider Room GainEF2241 Block Diagram EN Echo Canceller, Noise CancellerConnector Pinouts EF BusInput/Output Remote Control Port Instructions Connecting Unbalanced RCA to Balanced Mini PhoenixMaking AN EF BUS Terminator Additional Notes Warranty Information RMA# Must be on packageWhat this warranty does not cover State Law RightsEcho Canceller Definition of TermsAcoustic Echo Crosspoint Mix Minus BusNOM Attenuation NOM Bus Presets Room Gain NOMDefinition of Terms Index NOM Index Page 1725-80098-001-C
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