ATCOM AX-400P Installation Guide download pdf (Page 27)

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7. Echo Cancellation

Echo is a big problem in VoIP and the most possibility echo problem in our system is

the making outbound calls via an IP Phone. Below is several ways to improve our

voice quality.

Use ztmonitor to trace the echo

Run ztmonitor -1 v to trace the port1 and you will see:

( # = Audio Level * = Max Audio Hit )

<----------------(RX)----------------> <----------------(TX)---------------->

#####* #######################*

You can see the RX voice level and TX voice level when you are talking and if we

mute one side for example mute the RX PSTN side and the there should be total silent

in the RX side. In this case, RX level should be 0 and if we are talking on the TX side

and see there are some audio on the RX side, it means there are echo in our talking.

The first way to reduce the echo is modify the RX and TX gain, we can go to

/etc/asterisk/zapata.conf and adjust the rxgain and txgain. Modify and modify up to

the echo is acceptable.

Remember you need to go to the asterisk CLI to reload the chan_zap.so module after

every time you modify the file.

Use FXOTUNE tool to configure the line impedance

Every country has different PSTN line impedance. If the line impedance doesn’t

match, then you will experience more or less echo. Fxotune utility is a tool to auto

configure the line impedance of your PSTN line and set the corresponding echo

coefficient for your line

This tool is installed default in Trixbox. Use the SSH tool to access the Trixbox and

run :

asterisk –vvvvvgrc

stop now //before running the fxotune. You need to stop asterisk

fxotune -i 5

The system will test the PSTN line impedance and set the corresponding echo

coefficient in the /etc/fxotune.conf file. This will take about 20 minutes for to do it.

Notice, It will test all the FXO ports in your system , if you don’t have the PSTN line

connect to this port , it will generate wrong data in the /etc/fxotune.conf file.

fxotune –s // to apply the setting

Run the asterisk and then you will find that the voice is better than before

More info about this utility, please refer www.voip-info.org, you can find more detail

of this tool.

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ATCOM AX-400P Installation Guide Page 27