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Sheet music to MIDI: what the file can tell you and what it cannot

By Taekyung Lee · 2026-10-10

Every demo song on this site, and every page you convert, comes with a MIDI file. People expect it to sound like a recording and are surprised when it sounds like a music box. That is what MIDI is. Here is what is actually in the file, what gets lost on the way from paper to file, and the three ways it is genuinely useful for learning a piece.

What a MIDI file is

A MIDI file is not audio. It is a list of instructions: at time 0, press key 60 (middle C) at this loudness; at time 480, release it; at time 480, press key 62. A player program reads the list and makes the sounds with whatever instrument it has, which is why the same file sounds like a grand piano in one app and a toy in another. The file is tiny, a few kilobytes for a whole piece, and it can be slowed down without changing the pitch, which is the property that makes it useful for practice.

What gets into the file from the page

When Notalo converts a page, each detected notehead becomes one note in the file. Its pitch comes from the staff position, the clef and the key signature. Its start time comes from its horizontal position in the bar: notes are sorted left to right, and each starts when the previous one in the same hand ends. Its length comes from the notehead shape (hollow or filled), the flags or beams on its stem, and a dot if there is one. The right hand goes on one track, the left on another, so you can mute either in most players.

Tempo is whatever you ask for; the page does not say. The demo songs are set to a sensible speed for each piece and your conversions default to 90 beats per minute. Loudness is the same for every note. There is no pedal, no accent, no ritardando at the end of the phrase.

What gets lost

• Rests. We do not yet detect rests, so a rest is filled by the previous note being held longer. The timing of everything after it stays right, because note lengths are measured from the page positions; only the silence is missing.
• Ties. A tie joins two notes into one longer note. We play them as two notes, re-struck. On a piano this is audible; on a sustained instrument it is the difference between a held note and a repeated one.
• Triplets and other tuplets. Three notes in the time of two are written with a small 3 over the beam. We do not read the 3 and play them as ordinary eighths, so a triplet bar runs long. Classical pieces with triplet accompaniments (the Moonlight Sonata is the famous case) are the ones where this matters; our easy version of it is written in 12/8 precisely to avoid it.
• Dots on photos. On a clean PDF we read the dot after a dotted note almost every time. On a phone photo the dot often merges with a staff line and the note plays at two-thirds of its length. Pitches are unaffected.
• Grace notes, trills, ornaments. Not read. A trill plays as its main note.
• Repeat signs, first and second endings, D.C. al Fine. Not read. The file plays the page once, top to bottom.

So a converted MIDI file is a reliable record of which notes are on the page in which order, a good record of their relative lengths on clean input, and a poor record of silence, articulation and form. That is a lot more useful than it sounds, as long as you know which parts to trust.

How to use it to learn a piece

1. Hear the tune before you can play it

Most beginners' mistakes are not wrong notes but wrong rhythms: holding a half note for one beat, rushing through a dotted figure. Hearing the file once, even at music-box quality, fixes the rhythm in your ear before your hands get a vote. Play it at the written tempo once, then at half speed while you follow the letters on the image.

2. Loop the bar you cannot play

Every decent MIDI player can loop a region. Loop the two hard bars at 60% speed and play along until you can do it three times running, then move the loop forward a bar. This is what a teacher does with a metronome and it works better with a sounding reference than with clicks.

3. Mute one hand

Because the two hands are on separate tracks, you can mute the right hand and play it yourself against the file's left hand, which is the hardest part of piano music to self-supervise: you can hear immediately when your hand falls behind the accompaniment. Then swap.

Players that do this

On a phone, any free MIDI player with a tempo slider will do; on a computer, MuseScore opens a MIDI file as a score (expect it to guess the note lengths and sometimes guess wrong), and most digital audio workstations open it as a piano roll. If the player shows a piano roll, you get a bonus: the notes are drawn as bars on a keyboard, which is a third way of seeing the same music next to the staff and the letters.

A note on the demo songs

The MIDI files for the demo songs are made the same way as your conversions: we render the score, run the detector on it and build the file from what it found, not from the score's own data. We do that on purpose, so that the files are an honest sample of what the converter produces on clean input. Where a demo file has a wrong length, that is a detector error, and the test set that catches it is public in the repository.

Written by Taekyung Lee, a self-taught pianist (four years, no lessons) who built Notalo for personal practice. About · Instagram

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