How to fix MIDI timing

Diagnose the timing before you quantize

Open the file and look at a short loop. Are the notes consistently late, randomly loose, or drifting over time? Consistent lateness often points to the source export or a tempo mismatch. Random looseness points to the performance. Drift points to a tempo map or PPQ problem.

Check the tempo map and the PPQ before changing notes. A file exported at the wrong tempo can look perfectly quantized on the grid while sounding wrong in real time. A file with several tempo changes can also make a single quantize grid misleading.

Choose a grid that matches the music

A quarter-note grid is for simple material, an eighth-note grid for common pop and rock phrasing, and a sixteenth-note grid for faster rhythmic detail. A thirty-second-note grid is rarely necessary unless the part contains fast ornaments or programming.

Do not choose a grid because it is the smallest available. A sixteenth-note grid applied to a swing phrase can erase the swing, and a quarter-note grid applied to a trap hi-hat pattern will destroy the rhythm. Match the grid to the intended subdivision, not to the density of the notes.

Quantize starts and ends together

EditMIDI quantizes both note starts and note ends. If the end rounding would collapse a note to zero length, the editor keeps it at least one tick long. That prevents invalid notes, but it does not guarantee a musical articulation; check the piano roll after the pass.

If the part has a deliberate legato or staccato shape, fix the note lengths after quantizing. A quantize pass can make every note end on the grid, which may be too short or too long for the phrase. The note-length tool can restore a percentage, legato, or staccato feel.

Restore feel with controlled variation

A strict grid can sound mechanical even when the notes are correct. A small humanize pass adds bounded timing and velocity variation without changing note lengths. Keep the timing range small, compare a short loop, and use the same seed if you want to reproduce the result.

Humanize is not a substitute for a good performance. If the source timing is already expressive, quantizing and humanizing it again can make it worse. Use the smallest intervention that solves the actual problem.

Check tempo and note length after the fix

After quantizing, play the phrase against a metronome and against the original. Listen for notes that now start on the grid but end too early, and for chords that lost their slight spread. A timing fix should make the phrase clearer, not merely align the pixels.

If the whole file still drifts, open the tempo map and compare it with the source audio. A single global BPM may be wrong for a file with rubato or several sections. In that case, fix the tempo map or split the file before applying another grid.

When not to quantize

Do not quantize a live performance that is intentionally expressive, a rubato piano part, or a MIDI capture of a human groove unless the goal is a deliberate mechanical effect. Quantize is a tool for alignment, not a universal quality setting.

If the file is a generated or converted MIDI with wrong notes, fix those notes first. Quantizing a wrong note only makes it wrong on time. Inspect the piano roll, repair the pitch and duration, then decide whether the timing needs another pass.

A timing checklist for generated MIDI

Generated files often contain a mixture of real musical timing and estimation noise. Start by checking the tempo map against the source audio. Then look for notes that are consistently early or late in one section. If only one lane drifts, fix that lane instead of applying a global grid.

After the timing pass, check note lengths, duplicate notes, and the final two bars. A file can look aligned and still have a clipped ending or a chord that rings too long. Listen to the transition into the next section, because that is where a small timing error becomes obvious.

• Compare the tempo map with the source before quantizing.
• Fix one drifting lane before changing the whole file.
• Check the final bar and the transition into the next section.

What to do after the pass

Save the corrected MIDI as a new file and compare it with the original in the same session. If the new version is better, keep both for a day before deleting anything. If it is worse, undo or reopen the original and try a smaller change.

A timing fix is successful when the phrase is easier to follow and still feels like the same performance. If the notes are aligned but the life is gone, the grid was too aggressive. Step back to a smaller intervention, or leave the original timing alone.