Yealink VC400 Administrator's Manual page 286

Administrator's Guide for Yealink Video Conferencing Systems
Check whether the near site is muted.
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Check whether the system has enabled the auto answer mute feature.
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Check whether the system has enabled the auto dialout mute feature.
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Why can't I hear the other site clearly during a call?
Ensure that the speaker volume of the far site is not set too low.
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Muffled audio reception from the far side may be caused by highly reverberant rooms.
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Speak in close proximity to the phone.
Adjust the priority order for your audio codec if you have chosen a low-bandwidth audio
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codec to be first. For more information, refer to
For best results, ensure that the caller is using a Yealink video conferencing system. Audio
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quality from your video conferencing system will vary when calling a non-Yealink system.
Dust and debris may cause audio quality. . Do not use any kind of liquid or aerosol cleaner
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on the phone. A soft, slightly damp cloth should be sufficient to clean the top surface of
the phone if necessary.
Why is the voice quality poor?
Users may receive poor voice quality during a call, such as intermittent voice, low volume, echo
or other noise. It is difficulty to diagnosis the root causes of the voice anomalies. The possible
reasons are:
Users sit too far from or near to the microphone.
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The audio pickup device is moved frequently.
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Intermittent voice is probably caused by voice packet loss or jitter. Voice packet loss may
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occur due to network congestion. Jitter may occur due to information reorganization of
the transmission or receiving equipment, such as, delay processing, retransmission
mechanism or buffer overflow.
Noise devices, such as computers or fans, may make it difficult to hear each other's voices
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clearly.
Wires may also cause this problem. Replace the old with the new cables, and then
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reconnect to check whether the new cables provide better connectivity.
Why can't I view the local video image?
Check whether the near site camera is connected to the VC400/VC120 codec correctly.
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Check whether camera is powered on, and the LED indicator illuminates green.
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Check whether the camera is selected for the current video input source.
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Check the screen layout to see whether the remote video image is shown in full size.
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Audio Codecs on page 137.