Administrator’s Guide for Yealink Video Conferencing Systems290the phone if necessary.Why is the voice quality poor?Users may receive poor voice quality during a call, such as intermittent voice, low volume, echoor other noise. It is difficulty to diagnosis the root causes of the voice anomalies. The possiblereasons are: Users sit too far from or near to the microphone. The audio pickup device is moved frequently. Intermittent voice is probably caused by voice packet loss or jitter. Voice packet loss mayoccur due to network congestion. Jitter may occur due to information reorganization ofthe transmission or receiving equipment, such as, delay processing, retransmissionmechanism or buffer overflow. Noise devices, such as computers or fans, may make it difficult to hear each other's voicesclearly. Wires may also cause this problem. Replace the old with the new cables, and thenreconnect to check whether the new cables provide better connectivity.Why can’t I view the local video image? Check whether the local site camera is connected to the VC400/VC120 Codec correctly. Check whether camera is powered on, and the LED indicator illuminates green. Check whether the camera is selected for the current video input source. Check the screen layout to see whether the remote video image is shown in full size.Why can’t I view the menu? Check whether the Display1 port of VC400/VC120 Codec is connected to the HDMI port onthe display device.Why can’t I start a presentation? Check whether a PC is connected to the VC400/VC120 Codec. Check whether the PC is sending a signal. Check the call statistics to see whether the system is sharing content. Ensure that dual-stream is configured correctly. For more information, refer toDual-Stream Protocol on page 196.
