[asterisk-users] hum noise

[Rob Hillis]

Rilawich Ango wrote:
> My configuration is simple as below.
>
> SIP phone <-> asterisk <-> CISCO <-> T1
>
> Do you mean the hum noise is created by electric-magnetic field?
> Asterisk can do nothing to eliminate it?
>   
That would be my bet.  No, Asterisk can't do anything to remove EM 
noise.  That's up to you since EM noise can just about always be 
filtered out.  The most likely source is from telephone cables being run 
too close to power cables, fluorescent lights and so on.  Improper 
shielding of components inside your PC could also be your problem.

If your connection to the outside world is T1, it's unlikely to be an 
external problem. (digital signals aren't affected in this manner by EM 
interference)  It's possible the SIP phone itself is faulty - other than 
that, make sure your Asterisk box and Cisco gear aren't located right 
next to heavy duty power cables or transformers.