Title: Reducing the Echo on the PSTN line of SPA3102
Article ID: 5167
Experiencing echoes in the PSTN line is a common problem. This is because the SPA3102 passes calls from the PSTN to LINE1 by converting it to VoIP internally then converts it back to analogue. This process does not produce any echo, however, it can add about 30ms of latency to the call which later produces the echo.
Reducing the Echo on the PSTN Line
Step 1:
Make sure you are running the latest firmware and everything should be set to factory defaults or at least undo all the previous tweaking.
Step 2:
Disable all the echo cancellation functions of your SPA3102. These settings can be found on line 1 and PSTN line tabs of your SPA3102.
Echo Canc Enable = No
Echo Canc Adaptive Enable = No
Echo Supp Enable = No
Step 3:
Remove devices connected to your phone line except the SPA3000. This includes all the extension cables and splitters. These can cause impedance problems which leads to echoes.
Step 4:
Set the FXO port Impedance on the PSTN tab to 220+820||120nF and set FXS Port Impedance to 220+820||115nF as a starting point.
Step 5:
Look for Network Jitter Level on the PSTN Line tab and set it to low then look for Jitter Buffer Adjustment and set it to disable. This reduces the delay across your SPA3000.
NOTE: If you are using a poor quality VOIP service, go to the Line 1 tab and look for Network Jitter Level and set it to low and set the Jitter Buffer Adjustment from up to down. But if you are using a poor quality PSTN, set the Network Jitter Level to medium.
Step 6:
Go to the PSTN Line under Audio Configuration look for Preferred Codec and set it to your preferred settings and lock it in by setting the Use Pref Codec Only to yes. Adjust these settings if you’re accessing your PSTN line via VoIP from a remote network then go to Line 1 and set Preferred Codec with the same settings you set with PSTN Line. Under Preferred Codec Only set it no. These settings reduce your latency and may make the echo less obvious or easier to catch with the echo canceller.
Step 7:
Power cycle the SPA3000 by powering down the device. This sometimes fixes the problem especially after changing the physical phone wiring.
Step 8:
Make some test calls and observe if you can hear an echo. If yes, the problem could be that you’re sending too much power down the line and gets reflected back somewhere as an echo. Even if you have good wiring but you are too close to the mouthpiece, you will still hear an echo. To resolve this, you need to increase the level of Gain by going to PSTN and look for SPA To PSTN Gain and slowly adjust the level until you can clearly hear the person on the other line.
NOTE: If you enable Echo Supp Enable, you will negate these parameters. The echo suppression is just an automatic gain control and it is recommended that it be kept disabled.
Step 9:
Make a test call to someone with a phone that works via the SPA's PSTN line or call in to the PSTN line. If the remote party is hearing an echo, your phone may be loud and is experiencing feedback into the microphone. Lower the PSTN to SPA Gain until you can be comfortable hearing the person on the other line. If the remote user can still hear an echo, try using a different phone plugged into the SPA. If this solves the problem, your phone may not be working properly or there is an impedance miss-match between your phone and the SPA. Try changing the FXS Port Impedance to 600 on the Regional tab and change the FXO port impedance to 600 or global. If this doesn't help, change it back. The impedance will only affect what the remote party hears and it won't help remove the echo you are hearing.
Step 10:
After lowering the echo to a tolerable level, go back into the PSTN tab and enable the Echo Can Enable by selecting Yes. Check if the echo has improved. If the echo is tolerable at this level, leave the adaptive echo canceller off. You should have the echo level down to a level that can be filtered by the echo canceller. If you are using a sip device to talk through your PSTN line, you should probably do all the echo cancellation at that device and leave it switched off in the SPA.作者: bubblestar 時間: 2010-12-2 13:32
