Call distortion, clicks, pops, squeaks. Any ideas? UK/Telew

Hi everybody.

I’m a fairly recent noob to the world of * but have had an * server up and running in my office for the last 3 or 4 months. In a testiment to my general lazyness, it has taken this long for me to seek help on an issue that plagues everyone!!

We frequently seem to have incoming audio distortion on the lines served by *. I have three cheap, single channel FXO cards in my server which is run over NFS root and network boot. I didn’t really know the score when I purchased the FXO cards of eBay and they show up as “Wildcard FXO: Generic Clone” so this could be the root of my problems.

I’m in the UK and connecting to Telewest land lines.

I have uploaded a small WAV file that I managed to record via voicemail (which puts the whole SIP transport out of the loop - we use SIP to connect to a hardware phone and several (different) soft phones which all experience the distortion). It’s only small at around 150kb.

You can grab the file here:

It only seems to happen on incomming channels and the outgoing speach doesn’t seem to be affected in the same way.

Here is my zaptel.conf:


And here is my zapata.conf:


channel => 1,3

; Default context does not answer...

PS I have tried Kewlstart and Loopstart but both seem to be the same. I also cannot detect remote hangup but that is another issue :smile:

Thanks for any advice, it’s much appreciated.


I have exactly the same problem on my home Asterisk box, and I am quite sure by now that the cause is the x100p clone.

As far as I can tell the POTS interface in the US, in the UK, and in Germany/Austria (which is where I have any experience at all) is just sufficiently different for these cards, which are optimized for the US POTS interface, to work sub-optimally elsewhere.

The various parameters you can set in the zapata.conf file to tune the interface seem to work with the more expensive cards only.

I have now got a Sipura 3K adapter coming for my home installation, and will see whether this solves the problem; I also have a “proper” Digium POTS interface card coming for a different project and will compare sound quality there as well.

Ahh, your feedback would be greatly appreciated.

I reckon seeing as they are fairly cheap anyways, I will try and source an original x100p card (One of the clones I bought was duff anyway!!) and see if it fairs better too.

Please report back tho’ as judging by my time at the moment, it may take me a while to get round to it!!!

All the best


Beware your PC running the cards as well.

We found out (the hard way) that there is a broad selection of motherboards that do not gracefully handle Digium cards (most specifically the TDM400P 4-port cards and X100P cards).

For example, Dell 7th generation motherboards do not (SC420, PowerEdge 750, etc.) and you will hear the snap/crackle/pop as well as intermittent echo.

However, Dell Poweredge 830 runs like a champ straight out of the box (8th generation motherboard).

Besides the card, it can also be PC related.

Interesting, thanks DevGuy.

It’s a fairly old mobo in the machine to be fair, but nothing fancy, just an old Althon machine.

NFS may also be an issue I suppose but hard to tell without installing locally which I want to avoid to keep the maintenance lower!! (less disks to worry about!!)


I have the exact same problem with a P4 machine with several X100P card clones. I may try to put them in a different PC, but if it turns out that it’s the cards it would be nice to know.


(and I’m using them in the US, so I don’t think it’s related to being used in the UK)

Oh that’s some handy/interesting feedback Pete, thanks for that.

Hmmmm, what to try now?? Perhaps a different batch of clones seeing as they are only a few ££ each. I didn’t realise the original Digium cards are about $200 (according to someone I asked recently). I wonder if the extre $190 dollars is worth it?? :smile: (sorry Digium!)

I guess we can probably russle up a new mobo/cpu combo here to test too but dunno when!!