There's No Audio Inside a MIDI File
A MIDI file is a set of playing instructions: which notes to play, when, how hard, and on which instrument. Sheet music for machines, in effect. When you press play, your software performs those instructions through a synthesizer, and the sound you hear comes from that synthesizer, not from the file.
Converting MIDI to MP3 means recording one of those performances. This page does that for .mid, .midi and .kar files: upload the score, and you get the performance back as an MP3 that plays anywhere.
Why the Same File Sounds Different in Every Converter
If you've converted one MIDI with two tools and gotten two different-sounding MP3s, neither tool was broken. Each performed the score with its own synthesizer and instrument samples, so each recording came out different, the way two pianists give you two recordings of the same sheet music.
Most converters never say what plays their files. Here it is for ours: FluidSynth, using the FluidR3 General MIDI soundfont. Piano parts come out as FluidR3's piano, strings as its strings. Convert the same file twice and you'll get the same result twice, and you'll know why it sounds the way it does.
How to Convert MIDI to MP3
- Upload your .mid, .midi or .kar file, or several at once.
- Pick MP3 as the output format.
- Download each MP3 as its render finishes.
The file uploads to our servers, renders and encodes there, and comes back to you as a download.
The Volume Problem, and What We Do About It
MIDI files carry no loudness standard, so raw renders land all over the map. In a batch of five real files we tested, the loudest peaked 19.8 dB above the quietest. Played back to back, one track blasts and the next whispers. The quietest of the five needed a +24.1 dB boost to reach a normal listening level.
So we normalize every render by default: each track is raised until its loudest moment sits at -1 dBFS, just under the digital ceiling. Your MP3s come out at a consistent volume without clipping.
Expect the MP3 to Be Much Bigger Than the MIDI
Don't be alarmed when a tiny MIDI turns into a normal-sized MP3. One 2.7KB file in our tests became a 1.19MB MP3. The MIDI stored a page of instructions; the MP3 stores every moment of the resulting sound. That growth means the conversion did its job.
Karaoke Files Work Too, With One Catch
A .kar file is a MIDI with lyrics stored as timed text. It converts here like any .mid, but the words exist only as text for a karaoke player to display, so the MP3 contains the backing music alone. If that's your file, KAR to MP3 covers the details.
When MP3 Isn't the Right Target
MP3 plays on everything, which makes it the default. For editing you'll want uncompressed audio, for an iPhone ringtone you'll want M4R, and for a game engine you'll want OGG. The MIDI converter hub lays out every output we support and when each one fits.