Other possible Echo Cause

[Al Johnson]

On Monday 15 December 2008, Paul wrote:
> > It's possible, but the buzz is within the voice frequency range. If we
> > could characterise the buzz sufficiently it may be possible to remove it
> > by applying a suitable digital filter in the CPU, but a hardware fix is
> > certainly preferable.
>
> I was thinking a software noise gate would be preferable since it
> requires less computing.  Also, anyone tried sound proofing the mic
> with sound insulating foam to prevent the sound from traveling through
> the phone?

There's a noise gate in the Wolfson chip, but I never managed to get it 
working. The functions in the GSM chipset sound like a noise gate in 
operation too. A better low-computing method might be to monitor the GSM 
output and mute the mic if there is significant signal there. This approach 
is used by some VoIP handsets ad is very effective at preventing echo, but 
can be awkward as the other end can't hear when you interrupt them ;-)

The mic has rubber around it which seals the gap between the mic and the case. 
I haven't tried modifying this.