Aftertouch (or channel pressure) events are generated by a mechanical pressure sensor beneath some MIDI keyboards. These events can be used to modulate the synthesizer sound. All note events on a particular MIDI channel are affected. This means that applying pressure to one note in a held chord affects all notes in the chord.
Ch(annel): MIDI channel of an event from 1 to 16.
Num(ber): This column is unused, as aftertouch events only have one data byte.
Val(ue): Displays the amount of pressure on the keyboard (0 to 127).