Audio to MIDI in REAPER

What REAPER can and cannot do here

REAPER edits MIDI very well, but it does not detect pitch in audio and write notes from it. If you own Melodyne, REAPER hosts it through ARA and you can drag notes out as MIDI from there. Otherwise the job is: convert the audio outside REAPER, then import the .mid.

Render a clean source

1. Solo the track you want. One instrument or one voice converts far better than a full mix.
2. Make a time selection over the bars you want — somewhere between fifteen seconds and a minute.
3. Open File → Render. Set Source to Selected tracks (stems) and Bounds to Time selection.
4. Choose WAV at 44.1 kHz. Bypass reverb and delay on the track first if you can — tails smear note onsets, which is the most common cause of extra notes.
5. Note your project tempo. You will set it in the converter.

Convert

1. Drop the WAV into the audio to MIDI converter. It runs in your browser, so the file is not uploaded anywhere.
2. Select the section you want — up to sixty seconds per run.
3. Use the Original / MIDI switch while it plays. Loop the selection and listen for wrong pitches rather than reading the piano roll.
4. Set tempo to your REAPER project tempo before you export.
5. Download the .mid.

Import into REAPER

1. Place the edit cursor where the part should start — usually the same position your time selection began.
2. Drag the .mid onto an empty track, or select the track and use Insert → Media file. REAPER creates a MIDI item.
3. Add an instrument to the track’s FX chain. ReaSynth is enough to check the notes; swap in whatever you actually want later.
4. Double-click the item to open the MIDI editor and check the part against the original.

Two things worth knowing:

• Tempo. Depending on your preferences, REAPER may ask whether to import the file’s tempo. If your project tempo is already right, keep it. If the notes land at the wrong spacing, fix the tempo in the converter and export again rather than stretching the item.
• One track per file. The converter always exports a single track, so you get one item, not a spread of tracks.

Common problems

• Notes drift out of time as the item plays. Tempo mismatch between the exported file and your project.
• The part starts in the wrong place. The item is inserted at the edit cursor. Move it to where the time selection began.
• A cloud of short notes. Reverb or a noisy source. Raise minimum note length in the converter, and render the audio dry.
• Melody is right, harmony is missing. Expected on anything dense. Convert each instrument separately if you have the stems.
• Notes an octave out. An overtone read as a fundamental. Narrow the pitch range and convert again, or transpose those notes in the MIDI editor.

Afterwards

Treat the result as a draft of the part, not a finished MIDI performance. Fixing note ends, deleting artefacts and adjusting velocity in REAPER’s MIDI editor is normal, and still much faster than playing the part in again from scratch.