how can I influence the attack time when I am using
the sustain+short section strings. I know there is
controller 21 but how does this work on detail.
I noticed that the release time if affected.
(I don't want to use velocity because in my actual
case this would change the sound too much)
I would like to have the same attack like
using auto-alternate but if I take that
the notes are too short.
Controller 21 changes release length (check the manual). The attack is varied with the note-on velocity, and that is all it changes. You don't have to worry that it will change volume or sound. That's what controller 1 (mod wheel) is for.
Velocity 1 produces a slowish attack, velocity 127 a rather aggressive attack. If you want it slower, you can always program it with controller 1 (let the value rise from 0 to the appropriate volume during 1 or 2 beats or so, and you'll have a pretty slow attack). There is also a more aggressive patch: sustain+short AG. You can control the "aggression" via a controller
in GPO4, but not in earlier versions, I think.