Pitch Bend & Aftertouch
Adding pitch bending or aftertouch can add a lot of subtlety to an otherwise plain sounding midi region and help humanize it.
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Pitch bending and aftertouch both work the same way, through automation, by right clicking the MIDI track's header > Automation > Bender (or Pressure) > the channel to bend.
Using the Draw tool, as for all the automations, allows to create a gradual change from one drawn point to another. A line in the center produces no change to the pitch, while a line above the center will bend the pitch to a higher note and a line going under the middle will bend the pitch to a lower note.
The pitch change depends on the synth-plugin used. Common ranges are an change of either ± 1, ± 2 or ± 4 semitones for the range 0 to 16383. The range is usually defined by the soundfont for each instrument. A value of 8192, which is also the default, means no pitch change.
Aftertouch works very similarly, though the values are between 0 and 127. It should be noted that aftertouch differs from velocity, as aftertouch allows to slightly change the timbre or create a vibrato, while the velocity sets the power with which the note is played (e.g. on a keyboard, the key is hit).