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Appendix B: Echo Canceling
Typically media gateways, like OfficeMaster Gate, have a so called Echo Canceler. With separated signals for
receiving and sending (like with ISDN) no echo can occur on the line itself.
When is an echo happening?
On analog lines, inbound and outbound signals are processes on the same channel. The own signal is reflected
muffled and can therefore lead to an echo, usually of low strength. A noticeable amplification of this echo can occur
at intersections between analog and digital. Several physical phenomena occurring with older analog devices on the
other side can produce an echo. With conventional telephony (without VoIP) the echo will not be noticeable, as it
arrives with a very short delay. Only from approximately 30ms onwards, an echo is noticeable. VoIP by principle
has longer delays and therefore a noticeable echo can occur. In most cases, an Echo Canceler in the gateway can
eliminate that echo.
What corrections can the in-build Echo Canceler make?
With OfficeMaster Gate it is possible to reduce echoes to a certain degree. Through the implemented algorithms,
an echo of up to 128ms delay can be recognized and fixed. Normally, the Echo Canceler should remain deactivated,
as every manipulation of the voice signal will also change it slightly, potentially affecting the quality.
Further measures for dealing with echo
Extensive research of recorded conversations has shown another reason for echoes. With extremely quite echo,
that is not noticed because of its low volume, the following can occur: The Echo Canceler does not recognize the
echo, as it is on background noise level. It can occur though, that in the mediation server or Lync-Client, language
is recognized via the automatic gain control (AGC). The AGC would then drastically increase the volume of the
signal to ensure comprehensibility.
By activating “Voice Activity Detection” in the VoIP parameters, the so called “Silence Suppression” is activat
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ed. With this, voice data, that is not louder than the background noise level, is not passed on. No subsequent ampli
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fication of an extremely quite echo will occur. Experience has shown, that this solution is much more effective than
the activation of the Echo Canceler.
Summary of Contents for OfficeMaster Gate
Page 14: ...Chapter 2 OfficeMaster Gate Ferrari electronic AG Installation...
Page 22: ...Chapter 3 OfficeMaster Gate Ferrari electronic AG Configuration...
Page 70: ...Chapter 4 OfficeMaster Gate Ferrari electronic AG Advanced Configuration...
Page 80: ...Chapter 5 OfficeMaster Gate Ferrari electronic AG...
Page 90: ...Chapter 7 OfficeMaster Gate Ferrari electronic AG Appendix...
Page 91: ...ii www ferrari electronic de Appendix A List of Abbreviations...
Page 103: ...Chapter 6 OfficeMaster Gate Ferrari electronic AG Worth knowing...
