[asterisk-users] Noise on FXS ports (Sangoma)

[Stephen Bosch]

John Novack wrote:
> Since the OP said the noise was on FXS ports, Jorge's answer isn't
> relevant.
> After listening to  a wav file of the noise, it sounds to my old ears
> like a background hiss or so called "comfort" noise, except for a couple
> of short pops which I assume to be an open microphone.

Yeah, that's correct.

Sometimes the background noise warbles a bit. This is why I am wondering
about ground.

The background noise is too inconsistent to my virgin ears to feel like
deliberate comfort noise. I wasn't aware that these modules were
supposed to generate that kind of comfort noise. Usually sidetone is
enough to make the set feel live to the user.

> Assuming this isn't generated by the POTS set connected to the port, I
> guess you'll have to dig into the configuration.
> Some POTS sets generate a similar though more erratic noise, caused by
> carbon transmitters and defective varistors in the network, but that is
> ancient history.
> More modern POTS sets with electret transmitters could certainly
> generate a similar noise.
> I am assuming that several different sets have been tried with similar
> results.

I have tried:

a cheap AT&T set;
a refurbished Northern Telecom "Symphony";
a classic ITT Touch Tone set

All of them sound great when connected directly to the PSTN (okay, maybe
the cheap AT&T set sounds a bit tinny), so I'm confident the sound is
not coming from the sets themselves.

> My experience with the Sangoma A200, and in fact Digium 400 and Adtran
> channel bank FXS circuits all are very quiet, so this is a bit of a puzzle.

Well, that's reassuring, because it means a solution must exist.

I don't know what configuration changes I would make to solve this. My
gut feeling is that it's an electrical problem somewhere within the
system, but perhaps I'm reaching for that too soon; in any case, I
wouldn't know where to start even if we accept that it is an electrical
problem.

Is a dirty ground not a possibility?

Is there a way to test this card in another server without having to
install Asterisk on it? I want to see if the noise is coming off the PCI
bus.

-Stephen-