Polycom EF2241 manual Excessive Room Gain

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TROUBLESHOOTING

and the level of this signal that is reflected as the microphone input (after microphone amplification).

A

B

AEC

Room Gain = 20 log (B/A)

Excessive Room Gain

Figure 28. Room Gain.

If the electrical level of the reflected signal picked up by microphone is the same as the level of the electrical signal sent from the AEC to the loudspeaker output, the room gain of this microphone channel is said to be 0 dB. If the reflected signal picked up by the microphone is higher than the level of the signal sent to the loudspeaker out- put, that microphone channel has positive room gain. The more positive the room gain, the harder the AEC must work to determine which signal is an echo and which is a local speech signal.

Excessive room gain can be caused through a number of mechanisms:

1.The most common is excessive amplification of the remote (reference) signal at the local loudspeaker output. This may be explained as follows. If the reference signal is too low coming into the EF2241, i.e. the codec audio signal is too low, the room audio amplifier is usually used to compensate and bring the room audio to an acceptable level. For example, if the reference signal is 12 dB too low, the room audio will need to be amplified by approximately 12 dB to bring it to a rea- sonable listening level. This adds 12 dB to the room gain, which will most likely cause it to exceed the amplifier room gain limit (See “Verify Room Gain” on page 14). This situation can be remedied by applying enough gain to the codec, phone or program audio inputs (Inputs A-D) which will make up the Reference input signal so that the acoustic echo canceller (AEC) sees a good reference sig- nal rather than trying to compensate at the amplifier.

2.Another common cause of room gain failure is excessive microphone amplifica- tion. For example, if a microphone is "hot" by 6 dB, then the reflections of the loudspeaker output signal which are picked up by the microphone will be ampli- fied by 6 dB more than necessary. This adds 6 dB to the room gain, which may be sufficient to cause room gain problems. This situation could easily arise if, for example, the conferencing equipment is set up so that participants are too far from the microphone. In such a situation, after correct microphone setup the local microphone audio level may be too low because of the distance from the

VORTEX EF2241 Reference Manual

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Contents Vortex EF2241 Reference Manual Page Introduction Welcome How to Use This Manual IntroductionProduct Features Product RegistrationProduct Inputs Outputs Remote Control What’s Included PRE-INSTALLATIONTools Needed for Installation What’s Not IncludedEF2241 Front and Rear Panels PRE-INSTALLATION Mounting the EF2241 InstallationConnecting the EF2241 to Other Equipment North American RequirementTypical EF2241 Connections CodecConnecting Multiple Vortex Devices Device IDS on the EF BUSFactory Default Settings Preset Terminating the EF2241Off Presets Multiple Vortex Devices Pick a Standard Signal LevelCheck Surrounding Equipment Configure Program Audio Sources Input Settings Integrating the EF2241 Into Your SystemCalibration Set Levels on Line Input Channels Echo Canceller Reference for Multiple Vortex Devices SET UP the Phone InterfaceBuild Your Echo Canceller Reference Customize Setting for Your Particular ApplicationSetting up Bus ReferenceConfigure the Automatic Microphone Mixer Automixer ParametersGlobal Settings Automixer Settings for Multiple Vortex Devices Channel SettingsConfigure the Matrix Mixer Default SettingsBuilding Your System with Multiple Vortex Devices Configure the submatrix Assign Inputs Assign OutputsEF BUS Presets Other EF2241 FeaturesConfigure Your Echo Canceller Reference 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 MacrosNo microphones are gating Some microphones are not gating TroubleshootingAutomatic Microphone Mixer Too many microphones are gatingResidual Echo Echo Canceller ReferenceMatrix Mixer 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 Compliance USA and CanadaUS Telco requirements 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 Connecting Unbalanced RCA to Balanced Mini Phoenix Making AN EF BUS TerminatorInstructions Additional Notes Warranty Information RMA# Must be on packageWhat this warranty does not cover State Law RightsAcoustic Echo Echo CancellerDefinition of Terms 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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