[Asterisk-Dev] zaptel echo preload patch

[James Harper]

Here's my first cut at a patch to be able to preload the echo canceller
data, which should serve as a good starting point for certain types of
echo and greatly reduce the echo canceller training time.

Obviously this is only really going to work for situations where the
echo is relatively constant per call, eg between your FXO adapter and
the FXO.

The patch is against zaptel 1.2.1. I've tested it by building a debian
package out of it, and with it my asterisk setup might just pass the
wife test.

To use it, build as normal, then do:
make zt_ec_dump
make zt_ec_preload

which will give you the two userspace tools, put them somewhere useful.

Brief howto:

Preload:
#1 place a call (preferably to a number that you know has minimal echo
problems of its own), and wait for the echo to stabilise (5-30 seconds
for me).
#2 do 'zt_ec_dump -r -d 1 >echo_data_chan_1' to dump out the echo
canceller data.
#3 hang up the call (not necessary really :)
#4 do 'zt_ec_preload -d 1 <echo_data_chan_1'
#5 try another call the same number as in #1. You should notice that the
echo canceller is instantly fully trained, and as good as it would be
after normal training.
#6 try calling a few other numbers and report the results back to the
list as I'd be interested to know how it goes.

Misc:
zt_ec_dump has a few output options apart from '-r' for raw:
no option - print it out in a human readable format (not that you'd
really want to)
-c - csv
-t - tab delimited. I used this and csv for importing into excel to
check out what the figures looked like in a graph.
-g - very crude ascii graph.

Enjoy!

James

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