[asterisk-users] screeching noise on zap channels

[Steve Totaro]

On Mon, Apr 7, 2008 at 8:17 AM, Col Ferguson <asterisk at coltect.no-ip.com> wrote:
> I have been working on a system where sometimes the users get a horrible
>  screeching noise that gets louder, typically as a call is hung up.
>
>  The system has 2 analog astribank channels with 8 FXO and 56 FXS ports, and
>  2 SIP phones, Asterisk 1.4.18, Zaptel 1.4.9.2. It is using the oslec echo
>  canceller.
>
>  In my testing, I have only experienced it on hang up of a call, but some of
>  the users say they have heard it at other times. It sounds like feedback
>  building up. The Receptionist said she had taken about 40 calls this
>  morning, and had only heard it once.
>
>  Because of the nature of the noise I have heard, I suspect something with
>  the echo cancelling, but I have no idea where to start looking. Maybe it
>  would just be easier/quicker to try a different echo canceller.
>
>  There is no noticable echo during conversations.
>
>  No one has heard the noise between the 2 sip phones, but as it seems
>  intermittent, this may be irrelevant.
>
>  Any hints as to how to track this noise down ?
>
>  Thanks,
>  Col
>

Start by turning off echo can on your zap channels.  I have setup many
analog FXI systems that never needed echo can.

Thanks,
Steve Totaro