From owner-freebsd-multimedia@FreeBSD.ORG  Wed Feb 28 16:36:43 2007
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From: Hans Petter Selasky <hselasky@c2i.net>
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Date: Wed, 28 Feb 2007 16:36:10 +0100
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Subject: Re: Intel High Definition Audio + Skype - echoing
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Hi,

I have some opinions about echo cancelling:

1) Echo cancelling should be part of the kernel.

2) Extremely low sound latency causes the echo canceller to use more CPU! 
Something in the range of 25-50ms is Ok. This is because an efficient echo 
canceller process samples in blocks instead of sample by sample.

Here is the old sample by sample echo canceller that I use with ISDN 
telephony:

http://www.turbocat.net/~hselasky/isdn4bsd/sources/src/sys/i4b/layer1/i4b_echo_cancel.c

I'm currently working on a new and block based one that will be more 
efficient.

--HPS