Matt Fredrickson wrote:
On Fri, Aug 26, 2005 at 02:00:54PM -0600, Rich Adamson wrote:
Relative to the fxotune app, it would appear the app is specific
to the v2.4 kernels (/dev/zap*), which the v2.6 kernels don't use
It should with 2.4 and 2.6. 2.6 kernels with properly configured udev
rules should create the /dev/zap/* entries dynamically.
(but rather the udev equivalent). (When I had * running on a v2.4
kernel, the output from fxotune never deviated from all zero's. So
I'm assuming the default chipset values were already tweaked by the
chipset manufacturer to US telco lines. If that is true, then
running fxotune in the US has very little value.)
Sometimes in the US you still deal with line impedance issues. In fact,
I was told by an engineer that worked for the company that designs the
line interface part that the bulk of echo problems (with line interface
parts such as this) are related to AC impedance mismatches (which is one
reason why I haven't done the digital hybrid tuning portion of fxotune
still). It should work the same regardless of which kernel (2.4 or 2.6)
you are using.
Everyone has to deal with line impedance issues. The hyrbids in
exchanges usually use a compromise impedance, but there are tolerance in
the circuits. The lines themselves vary far more, especially if loading
coil, and other fudges have been used. To get pretty good hybrid
performance you always need to individually tune.
What you have to remember about hybrids is they are not there to give
great rejection. They are there to give enough rejection to prevent
howling. Nothing more. The telephone approvals specs in most places only
call for 12dB of suppression through a hybrid. The exchange specs tend
to use a slightly higher figure, but only slightly.
I don't follow why knowing that impedance mismatch is the problem has
stopped you making fxotune fix it. :-\ Where you the one who asked me
how to make fxotune work well on IRC? Someone asked a while ago, and
said they were working on a faster tuning algorithm for fxotune. I've
forgotten who.
If it doesn't, and you have udev setup correctly, something is fundamentally
wrong in the setup.
Regards,
Steve
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