What Is a .mid File? What to Do After Converting MP3 to MIDI

What a .mid file actually contains

When I built this converter, I had to generate SMF files from scratch in JavaScript. That meant understanding the format at a byte level. Here is what goes inside:

• Note On / Note Off events: Each detected note becomes a pair of MIDI messages. A Note On message says "start playing note X at velocity Y at time T." A Note Off message says "stop playing note X at time T2." The duration of the note is the difference between those two timestamps.
• Pitch values: MIDI uses numbers 0–127 for pitch, where 60 is middle C (C4). Each semitone is one integer. The pitch detection algorithm in this tool finds a frequency in Hertz, then converts it to the nearest MIDI note number using the formula note = 69 + 12 × log2(freq / 440). This is why a 440 Hz tone maps to note 69 (A4).
• Velocity: Each note has a velocity value (0–127) that represents how hard the note was struck. This tool uses a fixed velocity because the detector extracts pitch, not amplitude dynamics. This is one of the things MIDI cannot fully capture from audio — more on that below.
• Timing: Events are stored with delta times — the number of ticks since the previous event. The file header declares how many ticks per quarter note (PPQ), and tempo meta-events define the BPM. This tool writes a default tempo of 120 BPM with 480 PPQ, which is a standard combination that every DAW understands.
• Track structure: The SMF format supports multiple tracks, but this tool writes a single track containing all detected notes on MIDI channel 0. That is the honest output: one melody line, one track.

The file is binary, not text. If you open it in a text editor you will see garbage characters. If you open it in a hex editor, you will see the "MThd" header chunk followed by "MTrk" track chunks. Every DAW and notation program can read this format — it has been the standard since 1983.

How to open a .mid file in a DAW

The .mid file this tool produces is a Type 0 SMF (single track). Every major DAW can import it. Here is how in the most common ones:

GarageBand (Mac / iOS)

1. Drag the .mid file directly into the GarageBand timeline, or use File → Import.
2. GarageBand creates a new software instrument track and places the MIDI notes on it.
3. By default it assigns a piano sound. Click the track header to change the instrument.
4. Press play to hear the notes. Edit them in the Piano Roll editor (double-click the region).

Logic Pro

1. Drag the .mid file into the Tracks area, or use File → Import → MIDI File.
2. Logic creates an external MIDI track or software instrument track. If you want sound, make sure it is a software instrument track with a plugin loaded.
3. Open the Piano Roll (Command-4) to edit individual notes.

Ableton Live

1. Drag the .mid file into the Arrangement view, or double-click it in the Browser panel.
2. Ableton creates a new MIDI clip on a new MIDI track.
3. Drag an instrument from the Browser onto the track (e.g., a piano from Ableton's stock instruments).
4. Double-click the clip to open the Note Editor and edit pitches, timing, or velocity.

FL Studio

1. Drag the .mid file into the Channel Rack or Playlist.
2. FL Studio imports the notes into a pattern. Assign a generator (synth, sampler, piano plugin) to the channel.
3. Open the Piano Roll for that channel to see and edit the notes.

MuseScore (free notation)

1. Use File → Import → MIDI, or drag the .mid file into the MuseScore window.
2. MuseScore converts the MIDI notes into standard music notation on a staff.
3. You can edit the notation, add a title, print it, or export it as PDF or MusicXML.
4. This is the best free option if your goal is a printable score rather than audio production.

MIDI vs audio: the fundamental difference

This is the single most important thing to understand about a .mid file, and almost no MP3 to MIDI tool explains it:

An MP3 is a recording of sound. A .mid file is a set of instructions to create sound.

• MP3 / WAV / FLAC: Contains digitized sound waves — the actual air pressure variations captured by a microphone. When you play an MP3, you hear exactly what was recorded. The file size is proportional to the audio length and quality.
• .mid (MIDI): Contains note data — pitch, timing, velocity. When you play a .mid file, you hear nothing unless a synthesizer interprets those notes and generates sound. The same .mid file sounds completely different depending on which instrument you assign. A melody played through a grand piano plugin sounds like a piano. The same file played through a synth bass sounds like a bass. The notes are identical; the sound is not.

This is why a .mid file is tiny — a few kilobytes for a full song — while an MP3 of the same song is several megabytes. The .mid file does not store sound; it stores instructions. The sound is generated on the fly by whatever instrument you choose.

It is also why converting MP3 to MIDI is a one-way, lossy process. The MP3 contains the final sound (instrument, timbre, dynamics, room ambience, effects). The MIDI file contains only the notes that can be detected — typically a single melody line. Everything else is gone.

What MIDI cannot store (and what you lose)

When you convert audio to MIDI, several things from the original recording are permanently lost. This is not a limitation of this tool — it is a limitation of the MIDI format itself:

• Timbre and instrument identity: MIDI does not store what instrument was playing. A note is just a pitch number. The .mid file from converting a guitar solo does not say "this was a guitar." When you import it into a DAW, you choose the instrument — and it might not match the original. This is why converted MIDI often sounds different from the source audio.
• Expression and dynamics: MIDI velocity is a single integer per note (0–127). It cannot capture the nuanced dynamics of a real performance — the swell of a sustained note, the subtle accent on a downbeat, the breath of a saxophone player. The converter writes a fixed velocity because the pitch detector does not extract amplitude envelope per note.
• Pitch bend and microtuning: MIDI notes are quantized to semitones. A note that is slightly flat or sharp (a blues guitar bend, a vibrato that dips below a semitone) gets rounded to the nearest integer pitch. The converter does this rounding — a note at 442 Hz rounds to A4 (69), even though it is slightly sharp.
• Timbral changes within a note: A saxophone note that starts breathy and opens up, a guitar note that decays with a specific envelope, a synth pad that evolves over time — none of this is in the .mid file. MIDI has no concept of timbral evolution within a single note.
• Multiple instruments: Because this tool's detector is monophonic (as explained in why MP3 to MIDI cannot hear chords), a multi-instrument recording is reduced to a single melody line. The bass, drums, harmonies, and backing instruments are not in the output.

Going the other direction: MIDI to WAV

Once you have edited the .mid file in a DAW and assigned an instrument you like, you will want to export it as audio. Every DAW can do this — look for "Export Audio," "Bounce," or "Render." The result is a WAV or MP3 file that contains the actual sound of the instrument playing your MIDI notes.

If you do not have a DAW and just want to hear a .mid file as audio quickly, this site also has a MIDI to WAV converter that runs in the browser. Drop the .mid file in, pick a soundfont, and download the WAV. No DAW required.

Common questions about .mid files

Can I play a .mid file directly?

Not without a synthesizer. On older Windows versions, Media Player could play .mid files using the built-in Microsoft GS Wavetable Synth. Modern operating systems are less reliable for this — macOS no longer includes a default MIDI synthesizer, and most media players will not play .mid files without a plugin. The reliable way to hear a .mid file is to import it into a DAW or use a tool like the MIDI to WAV converter.

Why is the .mid file so small?

Because it does not contain audio. A 30-second melody might produce a .mid file of 1–3 KB. The same 30 seconds as an MP3 would be around 500 KB. The .mid file stores a few hundred bytes of note data; the MP3 stores 30 seconds of digitized sound waves at 44,100 samples per second.

Can I edit the notes after converting?

Yes — that is the main reason to convert MP3 to MIDI in the first place. Once the notes are in a DAW's Piano Roll or a notation editor, you can move them, change pitches, fix timing errors, delete wrong notes, add new ones, and change the instrument. This is the advantage of MIDI over audio: the notes are fully editable. You cannot easily change a single wrong note in an MP3 recording; in MIDI, it is a drag-and-drop operation.

What is the difference between .mid and .midi?

Nothing. They are the same format with different file extensions. Both are Standard MIDI Files. Some operating systems use .mid, others use .midi. DAWs accept both interchangeably.

What is General MIDI?

General MIDI (GM) is a standard that defines which program number corresponds to which instrument. Program 0 is Acoustic Grand Piano, program 24 is Acoustic Guitar (nylon), program 73 is Flute, and so on. The .mid file from this tool does not include a program change message — it just writes notes on channel 0. When you import it into a DAW, you manually choose the instrument. This gives you more control than if the file forced a specific GM instrument.

Practical workflow: from MP3 to finished MIDI

Here is the realistic workflow for using a .mid file after converting from MP3:

1. Convert: Go to hummingtomidi.com, choose your audio file, click Convert to MIDI, download the .mid file.
2. Import: Drag the .mid file into your DAW. A new MIDI track appears with the notes.
3. Assign an instrument: Load a virtual instrument on the track — a piano, a synth, a bass, whatever fits your project.
4. Audit the notes: Play it back. Listen for wrong notes, timing errors, or missing notes. These are expected — the detector is monophonic and approximate.
5. Edit: Fix wrong pitches by dragging them in the Piano Roll. Tighten timing by quantizing. Delete spurious notes. Add missing notes by hand if you can hear them in the original but the detector missed them.
6. Build around it: Use the corrected melody as a starting point. Add chords, bass, drums, or other parts around it. The MIDI melody is a sketch, not a finished product.
7. Export: When your project is finished, export the whole thing as audio (WAV or MP3).

Ready to convert your audio and get a .mid file? Open the converter now.