[asterisk-users] SIP to IAX2 with delayed echo
dplatt at radagast.org
Thu Nov 20 17:27:04 CST 2008
> Coming from outside the network, setting up for a couple rounds of
> NATting isn't going to work well. They are not seeing it between
> phones. Others, using the polycom phones have reported echo between two
> SIP on a 4ms ping trip.
Could this be due to a purely acoustic echo within the Polycom handsets?
I encountered a nasty echo / hollow sound when using a cheap USB
"telephone" to connect to my Asterisk system (via KPhoneSI). The
echoing was due to acoustic feedback - the handset body acted as a
very nice channel for sound waves from the back side of the
speaker down to the microphone cartridge.
I opened up the handset, added some damping materials (panel-
vibration-damping and soft-foam sheeting, left over from a
car stereo speaker installation I did), closed it back up,
and the echoing was gone.
You might not notice in some calls, if the Polycom phones have
silence-detection turned on for those calls and if the amount
of feedback falls below the phones' silence threshold. If
the phone silence-detection algorithm were turned off on
other calls, the echo would then be audible.
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