Why we do not give a number
A percentage would have to be averaged across recordings that have nothing in common: a solo piano melody, a vocal with vibrato, a distorted guitar, a live room recording with drums. Averaging across them produces a figure that describes no recording in particular. A score measured on a set of ideal sine waves describes only that set of sine waves.
We have not run a measured benchmark on this converter, so this page reports no measured result. What we can describe, without inventing data, is the mechanism: what the detector does with a waveform, where that mechanism breaks down, and what those failures look like in the note list you download. Those are statements about how the code works and about the MIDI format, not claims about a test score.
What we claim, and what we do not
We claim that the converter writes a downloadable Standard MIDI File, runs in your browser, tracks a single pitch at a time, and requires no upload or signup. We do not claim an accuracy percentage, a measured success rate, a processing time, or a ranking against other services. If a page quotes a specific accuracy figure, ask what was measured, on which recordings, and against what ground truth.
What the detector actually does
The file is decoded into a waveform in your browser. For each slice of that waveform, the detector uses autocorrelation: it looks for the time shift at which the signal repeats itself, and reads that period as a pitch. The pitch is then written as a MIDI note number with a start time and a length.
That mechanism has consequences you can reason about without a benchmark:
- It needs a clear fundamental. Autocorrelation finds repetition in the whole waveform. If a harmonic is stronger than the fundamental at a given moment, the correlation can lock onto the harmonic and report its pitch instead. That produces a jump to another note, or a jump to the octave.
- It tracks a single pitch at a time. Simultaneous notes produce a combined waveform with several periods. The detector returns a single pitch, so chords and full mixes collapse into a single melodic line. We explain this in why MP3 to MIDI can't hear chords.
- MIDI pitch is discrete. A MIDI file stores a note number, not a continuous frequency. A pitch that falls between neighbouring semitones has to be written as a single note number. Nothing in the file records where between them the original pitch sat.
- The writer uses a fixed tempo grid. Notes are placed on the tempo the file writer sets, not on a tempo detected from the recording. Rhythmic placement in the output is therefore a representation, not a measurement of the original timing.
Which inputs break it, and why
| What is in the recording | What goes wrong | Why |
|---|---|---|
| Drums, bass, or an accompanying instrument | Extra note events, or a melody that follows the wrong voice | The waveform contains several periodic components at once; the detector can only return a single pitch per slice. |
| Reverb or a live, resonant room | Notes bleed into each other; held notes appear lengthened | The tail of a note is still sounding while the next begins, so the repetition pattern does not reset cleanly. |
| Distortion or heavy processing | Octave jumps and semitone shifts | Distortion adds harmonics; a harmonic can outweigh the fundamental in the correlation result. |
| Audible hiss, hum, or background noise | Spurious short notes appear between the real ones | Noise introduces transient patterns that the detector can read as pitch changes. |
| Vibrato, slides, or an out-of-tune instrument | The output snaps to a neighbouring semitone | MIDI note numbers are discrete; a moving pitch has to be quantised to a single note number. |
| Very short notes and fast passages | Notes are merged or missing | The detector needs a slice of waveform long enough to find a stable period before the signal changes again. |
The common thread is that the detector does not understand music. It reads periodicity. Any condition that muddies the periodicity, or that puts several periodicities in the same slice, produces a predictable kind of mistake. We go deeper on the failing audio types in why MP3 to MIDI sounds bad on certain recordings.
What the format itself cannot carry
Some expectations cannot be met by any converter, because they ask for information the MIDI file does not store. A .mid file holds note-on and note-off events with note numbers and timing. It does not hold the sound of the original instrument, the singer's phrasing, the room, the lyrics, the key signature, or a printable score. Rendering the MIDI back to audio plays the notes you now have; it does not restore the performance.
If what you need is a page a musician can read, that is a different deliverable. See MP3 to MIDI vs sheet music for how these artifacts differ and what a notation step adds.
How to check the output yourself
Rather than trusting a figure on a page, run your own check on your own recording. It takes a conversion and a listen:
- Pick a recording with a clear melodic line. If your source is a full mix, listen for whether a single voice stands out.
- Open the MP3 to MIDI converter, choose the file, and convert. The file is decoded in your browser; it is not uploaded.
- Open the detected-note list on the result panel. Read it against the melody you hear in the recording. Look for notes you did not play, notes that are missing, and notes that land on a neighbouring semitone.
- Download the
.midand open it in a piano roll. Fix the wrong notes there — that is the intended workflow, not a failure of the conversion. - For a listening check, render the edited file with the MIDI to WAV converter and compare the rendered line with the melody in your recording. If they no longer match, the edit went wrong.
- If the result is unusable, change the input rather than the converter: use a cleaner take, a solo line, or a recording with less room sound, then convert again. The converter handles a single file per conversion.
This check gives you something no published percentage can: a verdict on the exact file you care about. Different recordings of the same melody can produce different note lists, and your ears are the ground truth for both.
What "good enough" means
A browser-based converter is useful for capturing the shape of a monophonic line and getting it into a DAW as editable events. It is not useful for an exact transcription of a full mix, for chord detection, or for a finished score. Expect to correct notes by hand. That is a property of pitch detection and of the MIDI format, not a shortcoming we can quote a number for and then wave away.
Bottom line
There is no accuracy figure here because we have not measured a figure and will not invent a figure. What we can tell you is which recordings make pitch detection fail, why each failure happens, and how to verify the output on your own file in a single conversion. Judge the converter by that check, not by a number on a marketing page.
Want to run the check on your own recording? Convert a clean single-line melody and read the detected-note list.
Try the MP3 to MIDI converter →