<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="MSHTML 6.00.5730.11" name=GENERATOR></HEAD>
<BODY>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>This may be commonly
known but I haven't come across it so here goes, maybe it'll help
someone:</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN
class=546020417-15012007></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>I have terrible echo
with asterisk 1.2, zaptel 1.2.12, and a TDM400P with 1 FXS and two FXO
modules. </SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>The Mark2 echo
canceller with Aggressive turned on was the only setting that would make it
acceptable. </SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>I found fxotune with
this zaptel version to be broken.</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN
class=546020417-15012007> </SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>I pulled the latest
fxotune.c and fxotune.h from cvs and recompiled zaptel.
</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>fxotune then ran but
I got the error: Could<FONT size=2> not fill input buffer - got -1
bytes, expected 4000 bytes Failure!</FONT></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>After two days I
installed a splitter to listen in and found out that fxotune wanted 18 seconds
of silence on the line but Bellsouth only gives 15 seconds.</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>The -m switch in
./fxotune -i -m 15 -vv -b 3 -e 4 -t 2 allowed the test to complete
successfully.</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN
class=546020417-15012007></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>Before tuning the
TDM400P with ./fxotune -s, I observed the echo percentage on the line
with ./fxotune -d -b 4 to be .32, a far cry from the .05 I
wanted.</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>After ./fxotune -s,
./fxotune -d -b 4 revealed an echo percentage of .075, still not good
enough.</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN
class=546020417-15012007></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>I remembered that
there is a DSL filter between this FXO module and the PSTN
to break out signal for my DSL modem. I removed it and plugged the FXO
straight in to PSTN.</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>After a rerun of
./fxotune -i -m 15 -vv -b 3 -e 4 -t 2 and a ./fxotune -s, </SPAN></FONT><FONT
face=Arial size=2><SPAN class=546020417-15012007>./fxotune -d -b 4 now reveals
.026 percent echo! </SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>It appears that the
DSL filter circuitry affects the .fxotune impedance test to the point that it
becomes ineffective (~.05 delta in my case)</SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN
class=546020417-15012007></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007>FWIW, I replaced the
filter and reran <SPAN class=546020417-15012007>./fxotune -d -b 4 and observed a
report of .11 percent echo, which I do not trust due to the filter's effect on
the circuit.</SPAN></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007><SPAN
class=546020417-15012007></SPAN></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007><SPAN
class=546020417-15012007>I eagerly removed the aggressive suppression and
restored the original echo canceller to be disappointed that the echo still
exists. So it is back to Mark2 with Aggressive.</SPAN></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007><SPAN
class=546020417-15012007></SPAN></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007><SPAN
class=546020417-15012007>If you hang a FXO module behind a DSL filter and
have high echo percentages or echo, this is a gotcha.</SPAN></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007><SPAN
class=546020417-15012007></SPAN></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007><SPAN
class=546020417-15012007>I'm now experimenting with zaptel 1.4 with similar
results, despite a new default echo algorithm. </SPAN></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007><SPAN
class=546020417-15012007></SPAN></SPAN></FONT>
</DIV>
<DIV><FONT face=Arial size=2><SPAN class=546020417-15012007><SPAN
class=546020417-15012007>Also, any tips on echo reduction from here would be
greatly appreciated, I'm out of ideas. My biggest fear is
installing a hybrid system in a client's office and to come across a
situation where I can't suppress echo..</SPAN></SPAN></FONT>
</DIV></BODY></HTML>