01In plain English
MIDI does not record sound. It records which notes were played, when, and how hard. That data can drive any virtual instrument, and every note can be edited afterwards.
02How it works
When you press a key on a MIDI keyboard, the keyboard does not send sound. It sends a short message saying which note, how hard you pressed, and when you let go. The software records those messages on a track as a list of note events, laid out in an editor that looks like a grid. You can drag a note to fix its timing, stretch it longer or change its pitch, and then choose which instrument plays it. Swap a piano for a string section and the same notes play through a different sound. Because it is just data, MIDI files are tiny. It works like sheet music that any orchestra can play, rather than a recording of one performance.
03Why it matters when you are choosing
MIDI is how most music is written in a DAW. Good MIDI editing makes it quick to fix timing, change a melody or swap instruments.
04What to check
Check the MIDI editor, support for your keyboard or controller, and whether the app includes instruments to play the notes.
05Where you will meet it
06Common questions
Is MIDI the same as audio?
No. Audio is a recording of sound. MIDI is a set of instructions about notes, timing and force. A MIDI track makes no sound until you assign it to an instrument. The advantage is that you can change notes and instruments afterward, which you cannot do with a recording.
Do I need a MIDI keyboard to make music?
No. You can click or draw notes with a mouse, or type them in using your computer keyboard. A MIDI keyboard makes playing parts faster and feel more natural, and an inexpensive one is enough to begin with, and most programs also accept keyboards from any maker.
Can I turn audio into MIDI?
Sometimes. Some tools detect the notes in a recording and convert them, and it works best on a single clean melody. It works poorly on dense mixes with many instruments, so expect to correct the result by hand and treat it as a rough sketch of the notes.