GoHigh MG3000-R, User Manual

Page: 83 / 135

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This section will describe the service principles and configure steps from service
function point of view.
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VOIP GATEWAY32 can provide excellent IP voice quality, supporting G.711A, G.711U,
G.729, G.7231, G.726 and iLBC etc. VAD, CNG and functions can reduce the bandwidth
occupation. System also supports Voice Gain setting and echo cancel functions.
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Fig 59
Echo caused by combined transmission imbalance
Echo is a very important factor which has a very big impact on the voice quality. The
breed-through delay when transport voice signal to receiver channel by mixed circuit (2/4 line
transform), or the reflection caused by the resistance mismatch, will cause the echo. In
general, echo always exists in PSTN network, and sometimes it is not a problem. In fact, part
of the phone signal will be coupled to receiver channel to generate side tone, which makes
speaker can hear his own voice. If without sidetone, the speaker would not be certain that
the other side can hear his voice or not and the dialogue would be very embarrassed. But if
do not control the echo, it will affect the users’ call experience in 2 ways:
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The bigger the echo is, the greater the interference is. In many situations, there
are low echo in the circuit, but the user can not feel it;

Echo delay will affect the voice quality greatly. Echo delay means the time
between the users speak and hear his own voice. If the echo delay is more than 25