RTS SIP-ISDN, Hardware & Software Manual, Page: 39 / 102

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• For each caller line, a separate Echo Canceller is available which can be set ON , OFF
or is activated automatically ( AUTO ) if required.
To configure the Echo Canceller, please select the desired line with your mouse and
press the button
Edit , which opens the configuration window.
To generally set the Echo Canceller off select Off .
If you always want to have the Echo Canceller activated, select Always ON . In
this case, no test tone to detect the echo is sent.
If the option Auto is selected, the Echo Canceller is switched on or switched off dy-
namically. The system sends a short test tone to determine if Echo Cancelling is re-
quired or not.
Via the button Set EC on/off/auto for all lines you can select the same operating
mode of the Echo Canceller for all lines.
Automatic Gain Control (AGC) Settings/Expander
The functioning of the AGC can be optimised via several parameters.
•
Threshold
: The
AGC
does not start before the signal exceeds the threshold value
selected under Threshold. The default setting is -30 dBu.
•
Level
: The level selected corresponds with the desired average level. Please consider
sufficient head room. The default setting is -12 dBu.
• Speed : Depending on the desired speed of the level adjustment ( Slow, Medium or
Fast ) the setting of the AGC speed can be configured here. The faster the AGC must
work the more noticeable are the inconsistencies. If the selected speed is too slow, the
caller signal is too low or too loud on average. The default setting is
Medium .
• An Expander turns down the caller signal automatically, if its level falls below a
certain threshold value. The aim is to completely filter out background noises of cal-
lers who are not currently speaking.The
Expander is activated by checking the re-
spective box.
• With the use of the Default Settings button, the default settings indicated above are
selected and the Expander is enabled.
NOTICE
In general, the use of the Echo Canceller is recommended. When a subscriber calls
with an
analogue telephone, a line echo is produced which can interfere with the in-
coming signal. Digital telephones (e.g. ISDN or mobile phones) do not produce these
line echoes. In this case an Echo Canceller would worsen the incoming signal. For
this reason the system sends a short test tone when a connection is established (only
in the
AUTO mode) and detects the level of the echo. If a certain threshold value is
not exceeded, the Echo Canceller is set off because the use of a digital phone on the
counterpart is anticipated. If the level is too high, the Echo Canceller is set on auto-
matically.
But: Echo Cancellers can only suppress echoes if the delay of the signal lies within a
certain scope. Telephone connections via satellite have such a long delay that the
Echo Canceller cannot work properly anymore.