What is MIDI?
MIDI (Musical Instrument Digital Interface) is a communication protocol for digital musical instruments, created in 1983. MIDI files (.mid) don't contain recorded audio — they contain musical instructions: which note to play, when, at what velocity, and on which instrument.
Think of it this way: MIDI is a score; an audio file (MP3, WAV) is a recording.
What's Inside a MIDI File?
- Note On/Off: which pitch starts or stops
- Velocity: how hard the key is pressed (0-127)
- Channel: which instrument plays (channels 1-16)
- Program Change: instrument selection (piano, guitar, drums...)
- Tempo: speed in BPM
- Control Change: volume, panning, sustain pedal, etc.
General MIDI (GM) standard defines 128 instruments and assigns percussion to channel 10.
MIDI vs Audio: Key Differences
| Aspect | MIDI | Audio (MP3/WAV) |
|---|---|---|
| Contains | Instructions | Recorded sound |
| File size | Very small (KB) | Large (MB) |
| Editable | Completely | Limited |
| Quality | Depends on synthesizer | Fixed |
| Transpose | Trivial | Requires processing |
| Change instrument | One click | Impossible |
What is MIDI Used For?
- Music production: recording keyboard performances in a DAW
- Karaoke: KAR files include synchronized lyrics
- Retro gaming: many 90s games used MIDI for music (Game Boy, SNES)
- Digital instruments: electric pianos, drum machines, synthesizers communicate via MIDI
How to Play MIDI Files
The sound depends entirely on the synthesizer rendering it:
- MuseScore (free): renders MIDI with high-quality virtual orchestra
- VLC: plays MIDI via FluidSynth
- DAW + VST instrument: assign a virtual instrument plugin
Converting MIDI to Audio
FluidSynth (Command Line)
sudo apt install fluidsynth
# You need a SoundFont (.sf2): GeneralUser GS, FluidR3_GM
# MIDI to WAV
fluidsynth -ni /path/to/soundfont.sf2 song.mid -F output.wav -r 44100
# WAV to MP3
ffmpeg -i output.wav -b:a 192k output.mp3
Timidity++
sudo apt install timidity
timidity song.mid -Ow -o output.wav
MIDI in Modern Music Production
- Record a keyboard performance into the DAW as MIDI
- Assign a VST plugin to generate actual audio
- Edit notes, tempo, and dynamics with full precision
- Render the final project to WAV/MP3 for distribution
Advanced Use Cases
Beyond casual conversion, modern audio formats cover highly specific professional scenarios. Music production: professional studios work with WAV or FLAC during mastering to avoid cumulative loss between passes — lossless format guarantees every modification is bit-perfect relative to the previous state. Streaming platform distribution: Spotify accepts WAV/FLAC at upload but re-encodes to Ogg Vorbis 320 kbps for Premium and AAC 128 kbps for free users; Apple Music uses AAC 256 kbps VBR; Tidal and Qobuz distribute FLAC for audiophiles. Professional podcasting: Apple Podcasts recommends AAC 128 kbps mono for voice (optimal efficiency); Spotify accepts MP3 192 kbps; master files are saved in WAV for future remasters. Audiobooks: Audible uses AAX (DRM variant of AAC) with variable bitrate by quality. Video games: many engines (Unity, Unreal) prefer OGG Vorbis for its royalty-free status and perfect looping support.
Best Practices and Professional Tips
Archival workflow: always keep a master FLAC or WAV of every important audio file. Lossy formats (MP3, AAC, OGG) are derivatives — you can always generate MP3 from FLAC, but never recover quality lost in the reverse direction. Bitrate selection: for music, MP3 320 kbps or AAC 256 kbps are indistinguishable from lossless on casual equipment; for podcast 96-128 kbps mono is enough. Sample rate: 44.1 kHz is the CD standard for music; 48 kHz for video; 96/192 kHz only adds value in professional production with studio monitoring. Metadata and cover art: always use ID3v2.4 with UTF-8 to ensure special characters (accents, ñ, Chinese symbols) display correctly in any player. Embed cover art at 600×600 px JPEG progressive — universally recognized standard format.
Compatibility and Technical Considerations
KaijuConverter processes audio files on dedicated cloud infrastructure with FFmpeg 6.x as the main engine and the best available codec libraries (LAME 3.100 for MP3, libfdk-aac for AAC, FLAC reference encoder, libopus for Opus). Processing is streaming — we don't wait to receive the full file before starting to process, significantly reducing perceived latency. We support files up to 200 MB with sample rates from 8 kHz to 192 kHz, depths of 16/24/32-bit (including float for professional editing), and configurations from mono to surround 7.1 when the destination format allows. Privacy: files are processed in isolated Docker containers, encrypted in transit with TLS 1.3, and automatically deleted with multi-pass overwrite after 2 hours. DRM: protected files (Apple Music DRM, Audible AAX) cannot be converted — DRM blocks access to the original stream. For those cases, you must obtain a legal DRM-free version before conversion.
Related conversions
Audio format pairs that come up most often: