[Asterisk-doc] RX and TX levels

[Randy Resnick]

I'm very confused about which is which in zaptel. I'd swear last time I 
adjusted these they seemed backwards in logic: RX changed the level when 
I spoke and TX changed the level of the outside caller? If this is right 
it means RX from the viewpoint of the FXS->FXO and TX FXO-FXS. If this 
makes no sense to you you already see the problem!

Is there anything about adjusting these? A clear paragraph would be 
really welcome.