Reaper MIDI Editor: Complete Guide to the Piano Roll

Reaper's MIDI Editor is where melodies, chord progressions, drum patterns, and bass lines come to life. Every note you program, every velocity you shape, and every controller curve you draw passes through this window. Unlike DAWs that treat the piano roll as a fixed feature with limited customization, Reaper's MIDI Editor is deeply configurable. You can change the tool behavior, remap every shortcut, adjust the appearance, and tailor it to exactly how you work. All of this ships with the $60 license.

For beat battle producers on Audeobox, the MIDI Editor is where speed matters most. Programming a drum pattern, writing a melody, and adjusting velocity curves under time pressure requires a tool that stays out of your way. This guide covers every essential technique for working in Reaper's piano roll, from basic note entry to advanced humanization and CC lane automation.

Opening the MIDI Editor

To open the MIDI Editor, double-click any MIDI Item in the arrange view. If you do not have a MIDI Item yet, create one by selecting a track and going to Insert > New MIDI Item or by drawing in the arrange view with the pencil tool while a MIDI track is selected.

The MIDI Editor can open inline (within the arrange view) or as a separate floating window. Configure this in Options > Preferences > Editing Behavior > MIDI Editor. The floating window gives you more workspace; the inline view keeps everything in context. For battle production, the inline view is usually faster because you never lose sight of your arrangement.

You can also open the MIDI Editor with Ctrl+Alt+E (Windows) or Cmd+Option+E (Mac) after selecting a MIDI Item. If the Item contains audio instead of MIDI, Reaper will offer to convert it.

Piano Roll Navigation and Tools

Zooming and Scrolling

Navigate the piano roll with your mouse wheel: scroll up/down to change the vertical view (pitch range), and hold Ctrl (Windows) / Cmd (Mac) while scrolling to zoom horizontally (time). Hold Alt (Windows) / Option (Mac) and scroll to zoom vertically on the note lanes. Middle-click and drag to pan in any direction.

Press Ctrl+Shift+Home (Windows) / Cmd+Shift+Home (Mac) to zoom to fit all notes in the view. This is the fastest way to orient yourself when you open a MIDI Item with an unknown range.

Tool Modes

The MIDI Editor toolbar contains the primary editing tools. Unlike some DAWs with separate tool buttons, Reaper's MIDI Editor uses context-sensitive mouse behavior. The primary modes are:

• Draw/Select mode (default) - Left-click in empty space to draw a note. Left-click on an existing note to select it. Drag to move.
• Marquee select - Right-click and drag to select multiple notes in a rectangle.
• Erase mode - Right-click on a note to delete it instantly.

You can customize which mouse button does what through Options > Preferences > Editing Behavior > Mouse Modifiers under the MIDI Editor context. Reaper lets you assign different actions to left-click, right-click, middle-click, and any modifier combination, giving you total control over how the piano roll responds to input.

Drawing and Editing Notes

Placing Notes

Click in the piano roll to place a note. The note's pitch is determined by the vertical position (read from the keyboard on the left), and the time position snaps to the current grid. The default note length matches the grid size. To draw a note longer than one grid division, click and drag horizontally.

To draw multiple notes quickly, hold down the mouse button after clicking and drag across multiple pitch positions. This paint-stroke approach is useful for rapid chord entry.

Selecting and Moving Notes

Click on a note to select it. Hold Shift and click to add notes to the selection. Draw a selection rectangle by right-clicking and dragging across an area. Selected notes highlight and can be moved together.

Move selected notes by clicking on one and dragging. Horizontal movement follows the grid snap. Hold Shift while dragging to constrain movement to one axis (horizontal only or vertical only). This prevents accidental pitch changes when you just want to adjust timing, or vice versa.

Resizing Notes

Hover over the right edge of a note until the cursor changes to a resize icon. Click and drag to change the note length. The start of the note stays fixed and the end point moves. To resize from the start of the note, hold Alt (Windows) / Option (Mac) and drag the left edge.

Note Velocity

Each note has a velocity value (0-127) visible in the velocity lane at the bottom of the MIDI Editor. Click on a velocity bar to change it. Drag across multiple velocity bars to draw a velocity curve. Higher velocity typically means louder, but many instruments also change timbre with velocity.

To set a specific velocity for new notes, hold Ctrl+Shift (Windows) / Cmd+Shift (Mac) and click in the velocity lane. To scale velocities proportionally, select notes, then go to Edit > Note velocity and enter an offset or multiplication factor.

Quantize and Grid Settings

Setting the Grid

The grid determines snap resolution for note placement and editing. Right-click the grid size dropdown in the MIDI Editor toolbar to choose common divisions: 1/4, 1/8, 1/16, 1/32, or triplet variants. You can also type a custom grid value.

Toggle grid snap on and off with Alt+S (Windows) / Option+S (Mac). Working with snap off lets you place notes at exact positions, which is useful for humanized timing. Toggle it back on when you need mechanical precision.

Quantizing Notes

Select the notes you want to quantize and press Q to open the Quantize dialog. This dialog offers precise control over how your notes snap to the grid:

• Grid - The target grid size for quantization
• Strength - 100% snaps notes perfectly to grid. Lower values move notes partially toward the grid, preserving some of the original feel.
• Start - Quantize note start positions
• End - Quantize note end positions (length)
• Position only - Move notes to grid without changing their length

For most production work, quantize at 80-90% strength to tighten timing while keeping a natural feel. Full 100% quantization works for electronic genres where mechanical precision is the aesthetic goal.

Humanize Techniques

Humanize is the opposite of quantize. It adds controlled randomness to note timing, velocity, and length to simulate the imperfections of a live performance.

Built-in Humanize Function

Select your notes and go to Edit > Humanize notes (or find it in the Actions List). Reaper's Humanize dialog lets you randomize:

• Position - Shifts note start times randomly within a specified range (in ticks)
• Velocity - Randomizes velocity values within a range you define
• Length - Varies note durations slightly

Start with subtle settings: position randomization of 10-20 ticks and velocity randomization of 10-15 units. Listen to the result and increase if the pattern still sounds too stiff. For drums, focus on position and velocity. For melodies, add slight length variation as well.

Manual Humanization

For more control, humanize by hand. Turn off grid snap and nudge individual notes slightly ahead of or behind the beat. Drag in the velocity lane to create natural dynamic curves. This takes more time but gives you complete control over where the human feel lands.

A classic technique is to push snare notes slightly behind the beat (2-10ms late) for a laid-back feel, and pull hi-hat notes slightly ahead of the beat for urgency. This push-pull creates groove that quantized patterns cannot replicate.

CC Lanes and Automation

CC (Continuous Controller) lanes at the bottom of the MIDI Editor let you automate parameters like modulation, expression, pitch bend, and any other MIDI CC message. These are essential for adding movement and expression to your MIDI performances.

Adding a CC Lane

Click the dropdown at the bottom left of the MIDI Editor (below the velocity lane) and select the CC number you want to add. Common lanes include:

• CC1 (Modulation Wheel) - Controls vibrato depth, filter sweep, or whatever your plugin maps to mod wheel
• CC7 (Volume) - MIDI volume control
• CC10 (Pan) - Stereo positioning via MIDI
• CC11 (Expression) - Dynamic volume control separate from CC7
• CC64 (Sustain Pedal) - On/off sustain
• Pitch Bend - Pitch wheel data with its own dedicated lane

Drawing CC Data

Click in the CC lane to draw individual CC points. Click and drag to paint a continuous curve. Hold Shift while drawing to create straight lines between points. For smooth sweeps (filter opens, volume fades, pitch bends), draw a line from start to end and Reaper interpolates between the values.

You can display multiple CC lanes simultaneously by clicking the lane header and choosing additional lanes. Each lane appears as a separate strip at the bottom of the MIDI Editor, giving you a full view of all active automation.

Advanced MIDI Operations

Transposition

Select notes and press Shift+Up/Down to transpose by semitone. Press Ctrl+Shift+Up/Down (Windows) / Cmd+Shift+Up/Down (Mac) to transpose by octave. For scale-aware transposition, install a ReaScript that constrains transposition to a specific scale.

Note Splitting and Joining

Split a note at the edit cursor by selecting it and pressing S. Join adjacent notes of the same pitch by selecting them and pressing J. This is useful for breaking sustained notes into rhythmic patterns or combining repeated notes into legato phrases.

MIDI Channel Filtering

Reaper's MIDI Editor can display and edit notes on all 16 MIDI channels simultaneously or filter to show a single channel. Use the channel filter dropdown in the toolbar to isolate specific channels. This is critical when working with multi-channel instruments like drum plugins that assign different sounds to different MIDI channels.

Ghost Notes and Multi-Item Editing

Enable ghost notes by going to the MIDI Editor menu Contents > Show MIDI Items on same track in other lanes. This displays notes from other MIDI Items on the same track as transparent overlay notes. You can see (but not accidentally edit) other patterns while writing, which is invaluable for ensuring your melody and bass line work together harmonically.

Battle MIDI Workflows

Speed Programming Drums

For the fastest drum programming under battle pressure:

1. Set the grid to 1/16 notes for detailed hi-hat work.
2. Open the MIDI Editor and switch to the Named Notes view (right-click the piano keyboard area). This labels each key with the drum sound name instead of a note letter.
3. Draw your kick pattern first (usually on beat 1 and 3 or variations). Hold Ctrl (Windows) / Cmd (Mac) and click to draw multiple notes at the same pitch quickly.
4. Draw snare on beats 2 and 4 (or beat 3 for half-time).
5. Paint hi-hats on every 1/16 step, then delete the ones you do not want for your pattern. Subtractive programming is faster than additive for complex hi-hat patterns.
6. Spend 15 seconds on velocity curves. Even a simple alternating loud/soft pattern on the hi-hats adds professional feel.

Quick Melody Writing

Enable the Scale Finder in the MIDI Editor (View > Scale/Chord or through the Actions List). This highlights scale-correct notes on the piano roll, preventing wrong notes during fast composition. Select your key and scale, and the piano roll grays out notes outside the scale. You cannot place wrong notes by accident.

For chord-based composition, use Reaper's Chord Track feature or program chords by placing notes in stacks. Select a chord, duplicate it with Ctrl+D (Windows) / Cmd+D (Mac), and transpose the duplicate to create your progression. A four-chord loop takes 20 seconds to program this way.

Frequently Asked Questions