Anyone using FR as a phone?
ml at e4net.com
Thu Jul 24 23:50:34 CEST 2008
Scott Derrick wrote:
> Come on! Blame the telcos for the Neo echo!! Thats stretching it.
> I've had numerous phones and about 4 different providers and NEVER had
> any repeatable echo, NEVER.
I've done quite a bit of work on VOIP on handhelds, and Echo is always a problem.
The solution was always to buy an echo cancellation library, I say buy because I never have found a
free one. The problem I found on ARM based handhelds is that they don't have an FPU and usually they
don't have enough CPU power to do real echo cancellation, so the libraries I have worked with for
ARM are usually echo suppression, which usually means detecting when someone is talking and dropping
the output volume (sort of half duplex like those old speaker phones).
I *suspect* that commercial cell phones have H/W echo cancellation built in via a dedicated DSP, but
there is no way to be sure unless you work for a cell phone company like Motorola, Nokia etc etc.
Landline phones generally do not have echo cancellation built in as the PO does the echo
cancellation, although higher end speaker phones will have echo cancellation built in.
I think some high end bluetooth headsets have either echo cancellation or echo suppression built in
which would help in our case.
I do not expect to be able to do echo cancellation on OM because there is no open source echo
cancellation I am aware of (the Speex codecs may have some) and it is doubtful anyone is prepared to
write one and make it open source.
Workarounds have been mentioned like using BT headset or tweaking volumes to minimize the echo.
Jim Morris, http://blog.wolfman.com
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