LocalMIDI

Audio to MIDI / Polyphony

Can an audio to MIDI converter turn chords into separate notes?

It depends on the converter. A monophonic tracker follows one dominant pitch at a time; a polyphonic transcription system attempts to identify several simultaneous pitches. LocalMIDI is explicitly a single-track, monophonic converter. It is designed for a clear melody line, not dependable separation of every note in a chord or full mix.

One pitch line is a different problem from a chord

When one note sounds at a time, the strongest repeating pitch can be followed from frame to frame and written as a sequence of MIDI note events. With a chord, several pitches overlap. Their partials can reinforce or obscure each other, and a pitch tracker may follow one component, jump between components, or return an unstable contour. Writing that contour as MIDI does not magically separate the original instruments.

Single melody and simultaneous chord have different pitch structureThe left side shows one note at a time in a monophonic line. The right side shows three overlapping notes in a chord, which requires separating simultaneous pitches.One pitch at a timeSeveral pitches togetherConcept diagram; not a measured transcription.
Original schematic: simultaneous notes require more than following one pitch contour.

Polyphonic conversion is not simply “monophonic, but with a wider note range.” The system must decide which spectral components belong to separate notes and when each begins and ends. A guitar chord, piano voicing, and layered synth can present different ambiguity even when their MIDI note counts are similar.

What LocalMIDI actually exports

The page describes its result as a single-track, monophonic Standard MIDI File. Its pitch analysis assigns one detected MIDI pitch to each analysis frame, then groups neighboring frames with similar pitch into note segments. The output builder writes those segments as note-on and note-off events; it does not run a source-separation stage that reconstructs every instrument in a mix.

That implementation can be useful when the task is to capture a lead melody, hummed line, or exposed single-note instrument. It is not a suitable promise for extracting a full piano chord progression or every line in a finished song. A MIDI file may still be produced from complex audio, but a file existing does not mean all simultaneous notes were identified correctly.

These statements describe the current LocalMIDI code and product scope, not a comparative accuracy result. No competitor was tested for this article, and no claim is made about which commercial or research model is “most accurate.”

Choose the source to match the job

  1. For a melody, isolate one lead line and start with a short phrase. This gives a monophonic tracker a clear target.
  2. For chords, try a tool that explicitly documents polyphonic transcription or instrument-specific extraction. Check whether it handles your source type, such as piano or guitar, rather than assuming “audio to MIDI” means every source.
  3. Listen to the result against the source and inspect the piano roll. A plausible melody is not proof that inner chord notes were recovered.
  4. If the goal is a playable arrangement, treat automatic output as a draft: compare notes by ear, correct missed or extra events, and keep the original audio for reference.
  5. Do not lower every detection threshold to force more notes from a chord. A single-pitch tracker can produce extra fragments without identifying the actual simultaneous pitches.

For LocalMIDI, use a clear melodic input and consider the output a monophonic sketch. If you need a chord transcription, the limitation is the task type, not merely a slider setting.

Related conversion questions

For a clearer source before a melody pass, see how to prepare audio. If short melody notes disappear, read the missing-note guide. The voice to MIDI guide explains what a sung line becomes in MIDI.