The Aftertouch mod source use the MIDI data of a played note.

• Aftertouch is controlled by pressing down on a held key of your MIDI keyboard.
• Aftertouch values can change while the note is held.
• The small graph
  Shows an adjustable curve that controls the mod source output level.

Input / Output Popover

Clicking on the small graphs will launch the input / output popover.

• The X axis of the graph shows the MIDI input value.
• The Y axis shows the modulation output value.
• Hover on the graph to show the output values at a given input level.
• You can adjust the curve by dragging the handles in the graph.