Fix the wrong tempo after audio to MIDI

What the tempo in the file actually does

Audio has no tempo, only time. The model reports every note as “starts at 2.31 seconds, lasts 0.4 seconds”. A MIDI file does not store seconds; it stores positions in beats. So the converter needs a tempo to turn one into the other, and it writes that tempo into the file.

The consequence is worth holding on to: the tempo you export with decides how the notes are laid out against a grid, not how they sound. Played at the tempo written in the file, the part is always as fast as your recording. The trouble starts when that tempo and your project’s tempo disagree.

Which problem do you have?

1. The part plays at the right speed but looks half or double on the grid

The tempo in the file is wrong by a factor of two, and your DAW kept it. A 90 BPM part exported as 180 plays correctly, but every beat spans two grid lines. Quantize then snaps to the wrong lines, and copying the part to the next bar goes wrong.

Fix: set Tempo in the converter to the real value and export again. Do not stretch the part in the DAW to compensate.

2. The part is faster or slower than the rest of the project

Your DAW ignored the tempo in the file and placed the notes by beat against the project tempo. Every beat is now the length of the project’s beat, not the file’s. The speed changes by the ratio between the two: 100 in the file against 120 in the project plays 20% faster.

Fix: export with the tempo of the project you are importing into. Then nothing needs to be scaled either way.

3. The part starts in time and drifts

The tempo is close but not exact, so the error grows with every bar. This is common when you guessed the tempo by ear or accepted an estimate on a recording that was not played to a click. After sixteen bars a 2 BPM error is already more than a beat out.

Fix: find the exact tempo (below) and export again. If the recording itself speeds up and slows down, no single tempo will hold, and the part needs to be conformed in the DAW instead.

How the estimate is made, and where it fails

The tempo shown in the converter is a hint, not a beat detector. It looks at the gaps between note starts, takes the middle one, treats it as one beat, and then doubles or halves the result until it lands between 70 and 180 BPM. Gaps shorter than 50 ms or longer than two seconds are ignored, and with fewer than four notes it falls back to 120.

That makes it wrong in predictable ways:

• Eighth-note parts read double. If most notes are eighths, the typical gap is half a beat, so a 90 BPM part reports 180.
• Slow, sustained parts read double or half. A chord-per-bar pad gives a gap of a whole bar, which is then folded into range at some multiple of the real tempo.
• Anything under 70 or over 180 cannot be reported. A 60 BPM ballad comes out as 120; a 200 BPM track as 100.
• Swing and triplets make the gaps uneven, so the median can land between values.
• Once you move the slider, the estimate stops updating for that file, so your value is not overwritten when you change the sensitivity afterwards.

Finding the real tempo

1. Use the number you already have. If the audio came out of a project, that project’s tempo is the answer. Nothing you can measure afterwards is as exact.
2. Otherwise tap along. Play the original and tap a tempo in your DAW or a tap-tempo tool for about thirty seconds. Round to a whole number unless you hear drift.
3. Sanity-check against the estimate. If the converter says 180 and your tapping says 90, you have the eighth-note case above. If tapping gives 90 and the estimate says 120, the part is probably not on a regular pulse and the estimate is not worth trusting.

Set it and export

1. Open the settings under the result in the audio to MIDI converter and find Tempo in the second group. It runs from 40 to 220.
2. Set it to the real tempo. Playback in the page does not change, because it plays the notes in seconds; what changes is the file you download.
3. Export, import into your DAW at the project tempo, and compare the part to the original on the first and last bar. If both line up, you are done.

If the DAW asks about tempo on import

Most DAWs offer to take the tempo from the file or keep the project’s. If the project already has the right tempo, keep it. If you are starting from the imported part, take the file’s, but check it first: a wrong tempo you accept at this step becomes the project’s tempo. The per-DAW steps are in the FL Studio, Ableton and REAPER guides.

Tempo and quantize

Quantize snaps note starts to a grid, so it is only as good as the tempo underneath it. Set the tempo first, then quantize, and keep the strength low if the take was played with feel. Quantizing against a wrong tempo moves notes confidently to the wrong places.