AVT MAGIC TH2, Hardware Manual

Page: 45 / 130

PAGE 45
W i n d o w s P C S o f t w a r e
• An
Echo Canceller
can be set on or set off separately for each channel.
Select the desired line with your mouse and press the button
Edit
, which
opens the configuration window (see Fig. 16). 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 dynamically. The system sends a short test tone to determine
if an Echo Cancelling is required or not.
Via the button
Set EC on/off/auto for all lines
you can select the same op-
erating mode of the
Echo Canceller
for all lines.
Automatic Gain Control Settings (AGC)/Expander
The correct functioning of the
AGC
can be optimised via several parameters.
•
Threshold
: The
AGC
does not start before the signal exceeds the thresh-
old value set here. The default setting is -30 dBu.
•
Level
:The level set here corresponds with the average desired level.
Please consider sufficient head room. The default setting is -12 dBu.
•
Speed
: Depending on the desired speed of the level adjustment (
Slow
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 set
speed is too slow, the caller signal is too low or too loud on average. The
default setting is
Medium
.
NOTICE
In general, the use of the Echo Canceller is recommended. When a subscriber
calls on the hybrid with an analogue telephone, a line echo is produced
which can interfere with the incoming signal. Digital telephones (e.g. ISDN
or mobile phones) do not produce these line echoes. In this case an Echo Can-
celler would worsen the incoming signal. For this reason the hybrid 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 automati-
cally.
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.
TIP
If your callers are put through by a Call-In-Center , you should use the option
Always ON
because otherwise the Echo Canceller is possibly not adjusted
correctly.
In the
Auto
mode, the test tone is namely send between the hybrid and the
Call-In-Center - and not, as required, between the hybrid and the caller. Since
most of the lines of Call-In-Centers are digital ones, the Echo Canceller would
be turned off internally. However, if the caller uses an analogue telephone,
disturbing echoes would be audible.