asterisk users - Dec 2012 - Audio feedback - where to troubleshoot?

We occasionally get a sort of feedback/echo noise on our phones here.  (Polycom
IP550 / Asterisk 1.8).  It lasts for about a second, and it's described by
users as 'jingle bells'.  It happens when people are using the
speakerphone, especially when it's on both ends.  It happens on internal
calls, so it's not something from the PSTN.

My theory is that the very sensitive speakerphone microphones in those models
are picking up small noises, and then picking up their own playback of the
noise, which leads to the feedback sound.  It repeats, which is why it sounds
like an echo.

I think turning rxgain/txgain down may make a difference, but I haven't
tried it yet.  Has anyone else experienced something similar?

Justin Sherrill - American Rock Salt
P: 585-991-6825 F: 585-991-6925 C: 585-298-6826

Justin Sherrill wrote:
> We occasionally get a sort of feedback/echo noise on our phones
> here.  (Polycom IP550 / Asterisk 1.8).  It lasts for about a second,
> and it's described by users as 'jingle bells'.
That's very appropriate for the season.  I just hope they're not
Todash Chimes.  ; )
> It happens when people are using the speakerphone, especially when
> it's on both ends.  It happens on internal calls, so it's not
> something from the PSTN.
> 
> My theory is that the very sensitive speakerphone microphones in
> those models are picking up small noises, and then picking up their
> own playback of the noise, which leads to the feedback sound.  It
> repeats, which is why it sounds like an echo.
Your theory sounds correct to me.  You've described acoustic echo and
that is the most prevalent type for internal VoIP calls.
> I think turning rxgain/txgain down may make a difference, but I
> haven't tried it yet.  Has anyone else experienced something
> similar?  
I believe rxgain and txgain only apply to DAHDI channels.  The first
thing I would try is reducing the speakerphone volume settings on the
Polycom IP550s.

Regards,

Matthew Roth
InterMedia Marketing Solutions
Software Engineer and Systems Developer