Sound Issue with distortion/reverberation

I am having voice quality problems on a small network of 4 handsets:
If I dial a extention and get voicemail the sound is good no echo no distortion/reverb. However if I dial an extension and it picks up handset to handset I get this distracting crackle like reverberation close to the end of every sentence (or anytime but not contant). The louder I speak the worse it gets. It also happens when I dial an outside line (POTS) via a Grandstream GXW4104. On an external call if I turn up the RX gain PSTN to PBX it get’s a worse.

This is a Virtualized Freepbx on a Virtual Box setup. 3.5 GB of Ram asign to VM.

Server is a 1 year old HP Proliant ML150 Xeon Prosessor total 6GB Ram on CentOS 5.x (PAE Kernel)

4 -Handsets Grandstream GXV3000 all upgraded to the latest firmware

2 - Gateways 4 port Grand Stream GXW4104’s connecting to 5 POTS lines (Telus is the telco her in Vancouver BC Canada) (both latest firmware)

NetGear 16 port 10/100/1000 Switch (4 Computers, 1 server, 2 gateways, 4 handsets, 1 Ricoh MF2550C Printer, 1 - Wireless access point)

There are 4 extensions setup 3000,3001,3002,3003

A couple of things:

  1. When you’re calling from extension-to-extension, you may get echo if the extensions are within earshot of each other, particularly if one or both of the telephone instruments is operating in speakerphone mode. I’ve seen this happen if the volume on the handset volume is set too high.

Have you set up echo cancellation for the POTS lines.

Finally, Virtual servers are fine for test boxes, but I’d never run a production telephone server on ANYTHING but a dedicated server. Using a virtual phone server can lead to unpredictable results.

You forgot to mention a few things.

  1. What version of Asterisk ? FreePBX ?
  2. How did you build it ? ISO or hand built ? And if ISO which one ?

Here is the version info
Asterisk 1.4.30
ISO is Elastix 1.6 latest stable

The Offices are close together however this is not your typical echo sound this is a distortion/reverberation that the users describe a crackle. I can hear it clearly as well I can make it worse by increasing the gain on the rx on the PSTN lines or by speaking louder into the handsets.

this is not when the phones are in speakerphone mode this happens when speaking into the handset.

Echo Cancel is setup on the Grandstream GXW-4104 gateways and when it is disabled you get echo loud and clear!

I am open to the possibility that the VM could cause unpredictable results but I am not convinced this is the case in this particular install. I suppose I could backup the settings and install on a separate box to be sure. Probobly worth the trouble to do so.

OK SO I thought I was getting the same problem extension to Extension but I guess in all the testing I was doing (Translate frustration) I was mistaken. The Issue turned out to be:

Tx to PSTN Audio Gain(dB):ch1-4:6; (-12-12, default 1)

Changed it to default and then settled on the following:

Tx to PSTN Audio Gain(dB):ch1-4:-2; (-12-12, default 1)