Need some Help: Voice Echo... not what you think


I need help on an issue here. We started off with a hosted FreePBX (which we tried pairing with a Netgear Router(customer owned) and EdgeSwitches) in digital ocean which was hacked a few weeks back and it was corrupted.(i guess the whole “droplet” was corrupted and we were on that droplet.

So we rushed out and installed a PBXact onsite and reconfigured all the phones. They are running Sangoma S700 phones. Latest firmware and PBXact up to date and changed out the Netgear with an EdgeRouter

Still had a few quality issues with choppiness. However the EdgeRouter was somehow receiving the keep alive packets on 5060 and returning them on 1064 (No idea how. I never configured an EdgeRouter before this was my first time) so the calls would drop after 30 seconds or after placed on Hold/Park.

Fast Forward a few days and I replaced with a Sophos UTM. Now everything sounds great to me. I can talk for 1/2 hour with no quality issues.

However although all quality issues cleared up for the most part, there is still one user who is remote. Uses his cell phone to call in. He is complaining of hearing an echo really bad when the office S700’s are on speakerphone. If they are on the handset or have S700 speakerphone low there are no issues. However if they blast it up high he hears an echo.

Construction of the Building:

20x20 rooms with very little furniture in each and 14ft ceilings. Solid Plaster on top of brick construction with Marble floors/carpet in some of the rooms. The rooms echo slightly when you talk in them normally.

Given the information above would you not conclude that the fact that the speakerphone is on high that it’s causing a bouceback of the voice into the speakerphone off the walls??

Maybe, but most Echo Cancellation could take that into account, assuming you are using EC on the external connections. If the phone is set loud enough and the mike is sensitive enough to pick up the ambient echo, you might see these issues.

A test would be to put some sound deadening in the conference room with the speaker phone. You don’t have to go crazy - hang some curtains around the room (or even quilts/blankets) and test again. If the echo is gone, you’ve figured it out. If not, then Echo Cancellation is your culprit.

As far as I’m concerned, EC is all dark magic. Maybe one of the really smart people can chime in on what else to check for.

Unfortunately, until you know the real source of the echo, you’re going to be flailing around in the dark trying to solve it.

Asterisk has no generic echo cancellation for sip channels, your phone might well do, given a 20x20x14 room then the maximum acoustic echo would be about 20 ms. (not particularly audible) , however any delay in the channel between the two endpoints will induce echo, this will always be a problem with cell phones , the connection will by nature have latency, that goes for both PSTN connections and soft-phone clients directly on the cell phone, and likely way more than the ~= 80 ms that will cause noticeable "distress’, make sure your QOS is well set to minimize such delays, but just don’t use speakerphones for a cell call unless you can successfully ‘tail’ a full 200ms in your EC software (that is generally really objectionable though)