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MIDI Files: Musical Instrument Digital Interface Format, Structure, and Conversion

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MIDI Files: Musical Instrument Digital Interface Format, Structure, and Conversion

PC By Pablo Cirre • Updated May 7, 2026

MIDI Files: Musical Instrument Digital Interface Explained

MIDI (Musical Instrument Digital Interface) is one of the music industry's most enduring technical standards. Finalized in 1983 by a consortium of synthesizer manufacturers (Roland, Sequential Circuits, Yamaha, Korg, Oberheim), MIDI defines both a communication protocol between hardware devices and a file format for storing musical performance data. Unlike audio formats (MP3, WAV, FLAC) that store recorded sound, MIDI stores instructions — which notes to play, how loud, on which instrument, with what timing. The same MIDI file sounds completely different when played back on a Roland synthesizer vs. a Yamaha grand piano plugin vs. a General MIDI soundfont.

What MIDI Is (and Is Not)

MIDI stores performance data, not audio. A MIDI file for Beethoven's Moonlight Sonata might be 15 KB. An equivalent WAV recording at CD quality is 40+ MB. The MIDI file says "play note C4 at velocity 80 for 1.2 seconds on channel 1" — it says nothing about what C4 actually sounds like. The playback device or software synthesizer supplies the sound.

This has profound implications:

Editability: Every note, velocity, timing, and instrument assignment is individually editable
Transposability: Transpose the entire piece by any interval without quality loss
Tempo flexibility: Change the tempo without affecting pitch (unlike speeding up audio)
Arrangement: Mute, solo, rearrange any instrument independently
Tiny file size: Complex compositions fit in a few kilobytes

What MIDI cannot do:

Capture subtle tonal variations that live performances have (breath, vibrato, bowing pressure)
Store audio effects like reverb or distortion
Guarantee identical playback across different synthesizers
Represent audio (drums recorded as audio vs. programmed MIDI sound completely different)

MIDI File Structure (SMF — Standard MIDI File)

MIDI files use the .mid or .midi extension and conform to the Standard MIDI File (SMF) format. An SMF file consists of chunks:

Header chunk: 14 bytes

4D 54 68 64  → "MThd" (Magic)
00 00 00 06  → Chunk length (always 6)
00 01        → Format (0=single track, 1=multi-track sync, 2=multi-track independent)
00 04        → Number of tracks
01 E0        → Division (ticks per quarter note = 480 here)

Track chunks (one per track, Format 1):

4D 54 72 6B  → "MTrk"
XX XX XX XX  → Track data length
[delta_time, MIDI_event...]

Each event in a track is prefixed by a delta time — the number of ticks since the previous event. This variable-length encoding is efficient for musical data where events are often close together.

MIDI Event Types

Channel Voice Messages (musical performance):

8n Note Off — stop playing note (channel n, note, velocity)
9n Note On — start playing note (channel n, note, velocity)
An Aftertouch — pressure after key press
Bn Control Change — CC messages (volume, pan, modulation, sustain pedal, etc.)
Cn Program Change — switch instrument (General MIDI instrument number)
Dn Channel Pressure — overall channel pressure
En Pitch Bend — pitch wheel ±8,192 semitones up or down

System Exclusive (SysEx) F0...F7: Manufacturer-specific messages for synthesizer parameter control (patch data, tuning, etc.).

Meta Events FF:

FF 51 — Set Tempo (microseconds per quarter note)
FF 58 — Time Signature
FF 59 — Key Signature
FF 03 — Track Name
FF 01 — Text Comment
FF 2F — End of Track

MIDI Channels and General MIDI

MIDI has 16 channels. Each channel can be assigned a different instrument via Program Change messages. Channel 10 is universally reserved for drums in General MIDI (GM) — percussion instruments are mapped to specific note numbers on channel 10.

General MIDI (GM) defines a standard set of 128 instruments (patches) that all GM-compliant synthesizers must support, using the same numbering:

0 = Acoustic Grand Piano
24 = Acoustic Guitar (nylon)
40 = Violin
56 = Trumpet
72 = Piccolo
80 = Lead 1 (square wave)

GM ensures that a MIDI file composed on one GM synthesizer sounds approximately correct on another — though timbre still varies significantly between manufacturers.

General MIDI 2 (GM2), Roland GS, and Yamaha XG extend GM with additional patches, variations, and effects parameters.

Converting MIDI Files

MIDI to MP3 / WAV (Synthesizing Audio)

This is the most common conversion request. It requires a software synthesizer to render the MIDI performance to audio using a soundfont or sample library.

Using FluidSynth (free, open source):

# Download a General MIDI soundfont first (e.g., FluidR3_GM.sf2)
fluidsynth -ni -F output.wav -r 44100 /path/to/FluidR3_GM.sf2 input.mid
# Then convert WAV to MP3
ffmpeg -i output.wav -c:a libmp3lame -q:a 2 output.mp3

Using TiMidity++ (free, open source):

timidity -Ow -o output.wav input.mid

Using MuseScore (GUI): File → Export → MP3 / WAV. MuseScore uses its own high-quality soundfont.

Quality tip: The output quality depends almost entirely on the soundfont. The free FluidR3_GM.sf2 (141 MB) sounds much better than the built-in Windows MIDI synth. Professional soundfonts (Vienna Symphonic Library, BBCSO, Spitfire) produce orchestral-quality output.

MIDI to Sheet Music / MusicXML

MIDI contains enough information (notes, durations, dynamics) to produce sheet music, though the result requires manual cleanup:

MuseScore: File → Open (MIDI file) → automatic quantization → Edit → Export → MusicXML / PDF

Sibelius / Finale / Dorico: All support MIDI import with quantization settings to clean up timing.

midi2abc: Converts MIDI to ABC notation (a text-based sheet music format):

midi2abc input.mid -o output.abc

MIDI to JSON / Text for Analysis

from mido import MidiFile
import json

mid = MidiFile('input.mid')
events = []
for track in mid.tracks:
    for msg in track:
        events.append({
            'type': msg.type,
            'time': msg.time,
            'channel': getattr(msg, 'channel', None),
            'note': getattr(msg, 'note', None),
            'velocity': getattr(msg, 'velocity', None),
        })

with open('output.json', 'w') as f:
    json.dump(events, f, indent=2)

MIDI in Music Production

Digital Audio Workstations (DAWs): Every professional DAW — Ableton Live, Logic Pro, Pro Tools, Cubase, FL Studio, Reaper — uses MIDI as its core performance language. Programmers record MIDI from keyboards, quantize timing, edit individual notes in a piano roll editor, then route each MIDI track to a software synthesizer or virtual instrument plugin.

Live performance: MIDI keyboards, drum pads, wind controllers, and guitar synthesizers send MIDI data to synthesizers, computers, or effects processors in real time.

Notation software: MuseScore, Sibelius, Finale, and Dorico use MIDI as input and output for playback and import/export.

Game audio: MIDI was used extensively in early game music (Nintendo's NES had hardware comparable to a MIDI synthesizer). Modern games use pre-rendered audio, but MIDI still powers some adaptive music systems.

MIDI vs. Audio Files

Feature	MIDI	Audio (WAV/MP3)
File size	Tiny (KB)	Large (MB)
Editable notes	✅	❌
Sounds like original	Depends on synth	✅ Exact
Transposable	✅ No quality loss	Requires pitch shifting
Tempo changeable	✅	Requires time stretching
Cross-platform sound	Varies by synth	Consistent
Captures live audio	❌	✅

MIDI is a composition and performance format. Audio is a playback format. Professional music production uses both: MIDI for arrangement and editing, audio for final mixdown.

Related conversions

Frequent conversions across the catalogue:

Frequently Asked Questions

MIDI files store performance instructions, not audio. The sound you hear depends entirely on the synthesizer or software rendering the MIDI. Windows uses the Microsoft GS Wavetable Synth by default, which sounds thin and low-quality. macOS uses a different built-in synthesizer. Professional DAWs use high-quality sample libraries. To get consistent, high-quality output, use FluidSynth with a good soundfont (FluidR3_GM.sf2 or better), or a DAW with a quality piano/orchestra library. The MIDI file itself is identical — only the renderer differs.

MIDI arquivos store performance instructions, not audio. The sound you hear depends entirely no synthesizer ou software rendering the MIDI. Windows uses the Microsoft GS Wavetable Synth by default, which sounds thin e baixa-quality. macOS uses a different built-in synthesizer. profissional DAWs usar alta-quality sample libraries. To get consistent, alta-quality output, usar FluidSynth com a bom soundfont (FluidR3_GM.sf2 ou better), ou a DAW com a quality piano/orchestra library. The MIDI arquivo itself is identical — only the renderer differs.

MIDI Dateien store performance instructions, not audio. The sound you hear depends entirely auf dem synthesizer oder Software rendering the MIDI. Windows uses the Microsoft GS Wavetable Synth by default, which sounds thin und niedrig-quality. macOS uses a different built-in synthesizer. professionell DAWs verwenden hoch-quality sample libraries. To get consistent, hoch-quality output, verwenden FluidSynth mit a gut soundfont (FluidR3_GM.sf2 oder better), oder a DAW mit a quality piano/orchestra library. The MIDI Datei itself is identical — only the renderer differs.

MIDI archivos store performance instructions, not audio. The sound you hear depends entirely en el synthesizer o software rendering the MIDI. Windows uses the Microsoft GS Wavetable Synth by default, which sounds thin y baja-quality. macOS uses a different built-in synthesizer. profesional DAWs usar alta-quality sample libraries. To get consistent, alta-quality output, usar FluidSynth con a bueno soundfont (FluidR3_GM.sf2 o better), o a DAW con a quality piano/orchestra library. The MIDI archivo itself is identical — only the renderer differs.

On KaijuConverter every file is processed inside an isolated container, encrypted in transit (TLS 1.3) and at rest, and automatically deleted after 60 minutes with multi-pass overwrite. We never train on, share, or analyze user content. For maximum privacy on extremely sensitive material, prefer offline tools (ImageMagick, FFmpeg, LibreOffice) that you control end-to-end.

You can convert MIDI to synthesized audio using a software synthesizer, but the result always sounds like a synthesizer — not a real instrument recording. Quality depends heavily on the soundfont or sample library used. Free options (FluidR3_GM.sf2, GeneralUser GS) produce passable results. Professional sample libraries (Vienna Symphonic Library, Spitfire BBCSO, EastWest Hollywood) can produce highly realistic orchestral audio, but cost hundreds or thousands of dollars. For truly realistic audio, the original piece needs to be performed and recorded by real musicians.

Você pode converter MIDI to synthesized audio usando a software synthesizer, mas the result always sounds like a synthesizer — not a real instrument recording. Quality depends heavily no soundfont ou sample library used. grátis options (FluidR3_GM.sf2, GeneralUser GS) produce passable results. profissional sample libraries (Vienna Symphonic Library, Spitfire BBCSO, EastWest Hollywood) can produce altaly realistic orchestral audio, mas cost hundreds ou thousands of dollars. para truly realistic audio, the original piece needs to be performed e recorded by real musicians.

Sie können umwandeln MIDI to synthesized audio using a Software synthesizer, aber the result always sounds like a synthesizer — not a real instrument recording. Quality depends heavily auf dem soundfont oder sample library used. kostenlos options (FluidR3_GM.sf2, GeneralUser GS) produce passable results. professionell sample libraries (Vienna Symphonic Library, Spitfire BBCSO, EastWest Hollywood) can produce hochly realistic orchestral audio, aber cost hundreds oder thousands von dollars. für truly realistic audio, the original piece needs to be performed und recorded by real musicians.

Puedes convertir MIDI to synthesized audio using a software synthesizer, pero the result always sounds like a synthesizer — not a real instrument recording. Quality depends heavily en el soundfont o sample library used. gratis options (FluidR3_GM.sf2, GeneralUser GS) produce passable results. profesional sample libraries (Vienna Symphonic Library, Spitfire BBCSO, EastWest Hollywood) can produce altaly realistic orchestral audio, pero cost hundreds o thousands de dollars. para truly realistic audio, the original piece needs to be performed y recorded by real musicians.

For 95% of use cases, yes — server-side ImageMagick, FFmpeg and LibreOffice produce identical output to the same tools on your laptop. Desktop software wins for: extremely large files (multi-GB), batch jobs of thousands of files, scripted pipelines, or content too sensitive to upload. KaijuConverter caps at 25 MB per file on the free tier (up to 2 GB on paid plans).

MuseScore (free) opens MIDI files and displays them as sheet music, allowing note editing in a piano roll or notation view. DAWs like Ableton Live, GarageBand (free on macOS/iOS), LMMS (free), and Reaper (discounted license) show MIDI in a piano roll for detailed note-by-note editing. For programmatic editing, the Python library mido or music21 provides full MIDI read/write access. The Aria Maestosa editor (free) is a lightweight dedicated MIDI editor for simple tasks.

MuseScore (free) opens MIDI arquivos e displays them as sheet music, allowing note editando em um piano roll ou notation view. DAWs like Ableton Live, GarageBand (free on macOS/iOS), LMMS (free), e Reaper (discounted license) show MIDI em um piano roll para detailed note-by-note editing. para programmatic editing, the Python library mido ou music21 fornece full MIDI read/write access. The Aria Maestosa editor (free) is a lightweight dedicated MIDI editor para simples tasks.

MuseScore (free) opens MIDI Dateien und displays them as sheet music, allowing note editing in einem piano roll oder notation view. DAWs like Ableton Live, GarageBand (free on macOS/iOS), LMMS (free), und Reaper (discounted license) show MIDI in einem piano roll für detailed note-by-note editing. für programmatic editing, the Python library mido oder music21 bietet full MIDI read/write access. The Aria Maestosa editor (free) is a lightweight dedicated MIDI editor für einfach tasks.

MuseScore (free) opens MIDI archivos y displays them as sheet music, allowing note editing en un piano roll o notation view. DAWs like Ableton Live, GarageBand (free on macOS/iOS), LMMS (free), y Reaper (discounted license) show MIDI en un piano roll para detailed note-by-note editing. para programmatic editing, the Python library mido o music21 proporciona full MIDI read/write access. The Aria Maestosa editor (free) is a lightweight dedicated MIDI editor para simple tasks.

Most format conversions are lossy by design — JPG, MP3, MP4, WebP all discard perceptual data to save bytes. Going through a lossy intermediate compounds the loss. To minimize visible/audible drift: convert from the original master, choose a higher quality setting, and avoid converting back and forth between lossy formats.

Format 0 (single track) stores all MIDI events in a single track, with channel assignments distinguishing different instruments — simple, widely compatible, but less organized. Format 1 (multi-track, synchronous) stores each instrument in a separate track, all synchronized to the same time base — the most common format for multi-instrument compositions and the format DAWs typically produce. Format 2 (multi-track, asynchronous) stores independent sequences that are not synchronized — rarely used, mainly for storing multiple independent song segments in one file.

Format 0 (single track) stores all MIDI events em um single track, com channel assignments distinguishing different instruments — simples, widely compatível, mas less organized. formato 1 (multi-track, synchronous) stores each instrument em um separate track, all synchronized para o same time base — the most common formato para multi-instrument compositions e the formato DAWs tipicamente produce. formato 2 (multi-track, asynchronous) stores independent sequences that are not synchronized — rarely used, mainly para storing multiple independent song segments in one file.

Format 0 (single track) stores all MIDI events in einem single track, mit channel assignments distinguishing different instruments — einfach, widely kompatibel, aber less organized. Format 1 (multi-track, synchronous) stores each instrument in einem separate track, all synchronized zum same time base — the most common Format für multi-instrument compositions und the Format DAWs typically produce. Format 2 (multi-track, asynchronous) stores independent sequences that are not synchronized — rarely used, mainly für storing multiple independent song segments in one file.

Format 0 (single track) stores all MIDI events en un single track, con channel assignments distinguishing different instruments — simple, widely compatible, pero less organized. formato 1 (multi-track, synchronous) stores each instrument en un separate track, all synchronized al same time base — the most common formato para multi-instrument compositions y the formato DAWs typically produce. formato 2 (multi-track, asynchronous) stores independent sequences that are not synchronized — rarely used, mainly para storing multiple independent song segments in one file.

Yes — KaijuConverter accepts multiple files in a single drop and returns a ZIP. For very large batches (thousands of files) consider command-line tools or our API: <code>find . -name "*.heic" -exec magick {} {.}.jpg \;</code> or similar one-liners scale to millions of files when run locally.