[Asterisk-Users] Small explanation of txgain rxgain statement please

[Steve Davies]

Hi,

I was just looking at:
http://www.asteriskdocs.org/modules/tinycontent/content/docbook/current/docs-html/x1695.html
regarding echo canceller tuning, and I noticed the statement

"Most people find that they need an rxgain level around 8.0 to have
good echo cancellation. The txgain setting varies from installation to
installation."

Which feels a bit wrong :) Could someone explain why increasing the
gain on the inbound zap leg (rxgain) would improve echo cancellation?
Of have I misunderstood the roles and meanings of rxgain and txgain?

Many thanks
Steve