Bruno it's in the Advanced menu in the manual.....
In addition to the Setup menu described previously are the MIDI and
Advanced menus. Hold the Mix button to enter the most recently used
of these menus. Hold the right arrow button to cycle to the next menu
or hold the left arrow to cycle to the previous menu.The current menu
name will show for a moment before changing to a parameter in that
menu and showing it’s value. The MIDI and Advanced menus are
discussed below.


1. Scroll Speed - Text scrolling speed in VoiceLive Touch can be increased
or decreased from the default value of 25. Numbers between 24 and 10
are faster and numbers between 26 and 50 are slower.