Toshiba Strata CTX Programming Manual page 409

Echo Cancellation and Volume Level Adjustments
Dealing with Echo Problems in General
The first step in isolating echo problems is to find the source. Usually only one party hears echo. If that's
the case, the echo source is the far end – if you hear echo, it is coming from the other party's side.
Example: if your local gateway is causing echo, you will not hear it because there is no delay in signals that
may bounce back to you. However, as the echo causing gateway is moved further away, echo becomes
more noticeable because the delay in the sound that is returned increases. Once you find out which end of
the network is causing the echo, check for devices such as cheap headsets or conference telephones – these
devices allow the earphone or speaker output to be feed back into the microphone to cause echo. Other
devices that cause echo are two-wire to four-wire converters and digital-to-analog gateways.
Echo Caused by Older CTX Analog PCBs
To provide optimum voice quality of IP telephones on Strata CTX systems, there are some compatibility
requirements that need to be followed when using analog CO line cards in the system.
• It is highly recommended to only use RCOU3A, RCOS3A, REMU1A (four-wire, not two-wire),
RDDU2A, and RGLU3A analog CO line interfaces in IP telephone applications. These PCBs provide
optimum speech quality for IPT1020-SD IP telephone connections.
• Do not use RCOU1A, RCOS1A, REMU1A (two-wire), RDDU1A, RGLU1A, or RGLU2A analog CO
line interfaces in IP telephone applications. These PCBs will work but will cause IP telephone users to
experience unacceptable voice quality and echo return loss.
Echo Reduction Adjustments
The items listed below can be adjusted to help eliminate echo. The below items will need to be tweaked,
case by case with trial and error, for each situation.
1. In WinAdmin, select IP Telephone > System IP data (Program 150-10); use "Tail length of Echo
Canceller" (set to different options and test).
2. In WinAdmin, select System > PAD table (Program 107) pad table; use IPT selection and reduce the
volume (increase Net Loss) to reduce the echo. This setting is a compromise between the acceptable
echo and volume loss levels (set to different options and test).
3. The IP telephone user taps the telephone Vol key (up or down), while on a call to cancel echo on a call-
by-call basis.
4. If using a Headset, the user can adjust the IP Telephone headset transmit volume level. In some cases,
lowering the headset transmit level can reduce echo.
Strata CTX Programming - Part 4: Appendices 04/03
Applications, Tips and Tricks
Echo Cancellation and Volume Level Adjustments
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