paolo67 wrote:
gain to get stable, I get more symmetric curves. There are three
positions for the time constant: 0.1, 1 and 10 seconds. Attack and
decay
times are unknown. I'm missing something: what setting should I choose
to perform the alignment?

Turn off the AGC. Adjust the gain so that it doesn't clip. Don't use
AGC during the alignment procedure.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."