Reaper MIDI editor

Create a MIDI item by either recording or cmd+click-dragging a section of the track length.¹

MIDI editor preferences can be accessed under Preferences.²

Change scrolling and zooming behavior in the Actions list and selected MIDI editor from the dropdown on the right.³

Right-click the grey area above the piano roll and mouse over to Options to change more about the MIDI editor.⁴

Other cool actions here.

Press J to join notes.⁵

Use the MIDI randomization script for fun.⁵

You can edit velocities globally by right-clicking and going to event properties. By using division or multiplication functions, you can compress or expand the velocities. Combine this with the filter to edit specific notes.⁶ You can do a similar thing with the JS MIDI Scaler/Compressor plugin.⁷

Humanize velocities with H.⁸

Drums

Right-click the grey area above the piano roll and mouse over to View to choose ‘Named notes’ for editing drums (I have this set to a toolbar button). Double-click a key to change note names. Hold command and drag to move notes around (doing so doesn’t interfere with the mapping).⁸ Under the View submenu, you can also hide unused and unnamed note rows.⁹

Right-click the grey area above the piano roll and mouse over to File to save note names to a file.⁹

Kenny Gioia shows how to create a ‘Drum mode’ toolbar button.¹⁰ Alejandro has a similar setup.⁸

Using MIDI grooves can help workflow.¹¹

Use the Explode MIDI note rows action to create stems for the drums.⁷