I think you are referring to Portamento?
This is when the notes slide from one to the next.
You can play with the Portamento settings on your synths to determine how fast the notes will slide (MIDI Controller #5).
Then, you press one key, say, at the low end of your keyboard and while still holding that key hit another one higher up. The portamento will start with the first key you pressed and eventually settle on the new tone.
Was this what yo meant?
For lots more info on audio visit the blog:
EarsandGears.com
It would be great to hear your questions there, so I could address them on the blog!