[asterisk-users] fxotune vs rxgain/txgain

[Matthew Fredrickson]

Noah Miller wrote:
> Well, that clears it up a little.  I think where I get confused is
> that sometimes using fxotune is called balancing the hybrid and some
> times using ztmonitor and adjusting the txgain/rgain settings is
> called balancing the hybrid.  Perhaps they both try to achieve the
> same goal, but through different means?

Not quite.  Gain adjustment affects volume levels of the respective 
direction you are adjusting (echo and all).  Balancing the hybrid via 
fxotune attempts to balance the hybrid in a manner so that the hybrid 
will remove as much of the echo as possible.

> This leads me to my other question - Are these two techniques mutually
> exclusive?  In some posts from Matthew Frederickson, it seems that
> they are, and that if you use fxotune, you should set your gains back
> to zero.  Some other people seem to suggest using both fxotune and
> adjusting gain levels.  I note that Stephen Bosch asked just this
> question some time back, and nobody was able to answer him.

These techniques are not mutually exclusive, I usually want people to 
use gain modification as the last step in trying to eliminate echo 
(after balancing the hybrid and making sure you are using a good echo 
canceller).

In the case of running fxotune, your zapata.conf software gain levels 
should not affect its operation.  If you are using any of the hardware 
gain settings (wctdm24xxp module parameters) you should normalize those 
to 0 beforehand so that they do not interfere with the calibration process.

-- 
Matthew Fredrickson
Software/Firmware Engineer
Digium, Inc.