MIDI is not audio
The most important thing to understand about MIDI is what it isn't. A MIDI file does not contain recorded sound. You cannot play a .mid file in a media player the same way you'd play an MP3 — at least, not without something to interpret it.
MIDI stands for Musical Instrument Digital Interface. It's a communication protocol and file format that stores musical instructions, not audio waveforms. A MIDI file tells a synthesizer (hardware or software) what notes to play, when, how long, and how loudly. The actual sound you hear depends entirely on what instrument or synthesizer is used to play those instructions back.
Think of MIDI like sheet music. A piece of sheet music tells a pianist which keys to press and when — but the sheet music itself makes no sound. MIDI works the same way: the data describes the performance, and a synthesizer brings it to life.
What's actually inside a MIDI file?
A MIDI file contains one or more tracks, each made up of a sequence of events. Common event types include:
- Note On — a note starts playing (includes the note number and velocity)
- Note Off — a note stops playing
- Program Change — switch to a different instrument sound
- Control Change — adjust a parameter like volume, pan, or modulation
- Tempo — set the playback speed in beats per minute
- Time Signature — define the rhythmic structure of the piece
Each note is identified by a number from 0 to 127. Middle C is note 60. A4 (the A above middle C, at 440 Hz) is note 69. These numbers map directly to piano keys and are universal across all MIDI equipment and software.
Because MIDI only stores instructions rather than audio, MIDI files are tiny — a full orchestral piece in MIDI format might be a few dozen kilobytes. The equivalent audio recording could be hundreds of megabytes.
MIDI vs MP3 vs WAV — what's the difference?
| Format | Contains | Editable? | File size |
|---|
| MIDI (.mid) | Musical instructions (notes, timing, velocity) | Yes — fully | Very small (KB) |
| MP3 (.mp3) | Compressed audio waveform | No (destructive) | Small (MB) |
| WAV (.wav) | Uncompressed audio waveform | No (destructive) | Large (MB–GB) |
MP3 and WAV both store recordings of actual sound. MIDI stores a description of a musical performance. This is why you can change the tempo of a MIDI file without it sounding weird — you're just telling it to play the same notes faster. Try that with a WAV and the pitch shifts too.
What is MIDI used for?
MIDI has been the backbone of music production since the 1980s and is still essential today:
- DAW production — almost all modern music production starts with MIDI. Producers lay down MIDI patterns and assign them to virtual instruments (VSTs), which generate the actual audio.
- Hardware keyboards and synthesizers — MIDI lets electronic instruments talk to computers and to each other. Playing a MIDI keyboard triggers a software instrument in your DAW.
- Transcription and notation — MIDI files can be converted to sheet music automatically, making them useful for learning and arranging.
- Game music and ringtones — MIDI was the dominant format for video game music in the 80s and 90s, and is still used in embedded systems due to its tiny file size.
- Live performance — MIDI controllers and sequences trigger sounds and lighting effects in live shows.
What does "channel 10" mean? (And why drums are special)
MIDI supports 16 channels — think of them as 16 separate instrument lanes. By long-standing convention, channel 10 is reserved for drums and percussion. On channel 10, each note number represents a different drum sound: note 36 is kick drum, note 38 is snare, note 42 is hi-hat, and so on. This convention is part of the General MIDI standard and is supported by virtually all synthesizers and DAWs.
When Filesmith generates a MIDI file with drums (Mode B or C), the drum track is automatically assigned to channel 10 so it routes correctly when imported into your DAW.
MIDI vs MID — is there a difference?
No. .mid and .midi are exactly the same file format. The shorter extension dates back to when operating systems had a 3-character limit on file extensions. Both are universally supported — use whichever your workflow prefers.
Can I convert audio to MIDI?
Yes — this is called audio-to-MIDI transcription or pitch detection. Software (or your browser, in the case of Filesmith) analyzes an audio file, detects the pitch frame by frame, and outputs a MIDI file with notes that approximate the original performance.
The quality of the result depends heavily on the source audio. Simple, clean, monophonic recordings (a single instrument or voice) transcribe well. Complex, dense mixes are harder to get right, though multi-track separation modes can help by isolating instruments before detection.
Filesmith can convert MP3, WAV, OGG, and other audio formats to MIDI, directly in your browser — no uploads, no software required.