This feature is only available in SoundPrism Pro - get it here:
Version 1.4 of SoundPrism Pro turns your iOS device into a 3D MIDI controller. Watch the following video for setup instructions. (Please note that since SoundPrism Pro version 2.2 the expression menu is now located within the preferences menu).
The new Humanize feature adds a human element to MIDI output by translating the impact of your fingers on your iOS Device into subtle changes in MIDI Velocity.