[Asterisk-Dev] zaptel echo preload patch

[Rich Adamson]

> 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.
 - snip -
> 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.

James,

I applied your patch by hand to SVN-trunk-r7661 compiled Dec 27th and 
followed the steps noted in your posting. The attached jpeg's reflect the 
graphs from TDM04b fxo calls using two pstn lines from Alltel (US) that are
roughly a 17,000 foot copper loops. (Four different pstn lines available.)
The two pstn lines (and graphs) are from one central office (echo.jpg)
and one Centrex central office (echo-4.jpg).

The four lines have been problematic since the x100p days, however with
this * code and MG2, echo has been very acceptable using zapata.conf
entries like:
 echocancel=yes
 echotraining=800
 echocancelwhenbridged=yes
 rxgain=5
 txgain=0

The current interface is a Rev H TDM card, with all source code stock 
svn-trunk including MG2 ec.

Using the preloaded ec values _did_ improve the EC speed without a doubt.

Questions...
1. Since the first major peak on the two graphs appear at different taps,
are the graphs suggesting two different copper lengths?
2. Do the y-axis peaks correlate roughly to "amount" of echo return?
3. Comparing your graph with mine, your peaks occur at roughly 28 taps
while mine are in the 37 to 43 tap range. Do you know what length of
copper your pstn line has?

Based on my limited testing thus far, I'd definitely support posting
the functionality as a feature for addition to svn trunk.

Rich
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