Convert MIDI to MP3, Free
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How to convert MIDI to MP3
MIDI files do not contain audio. They contain instructions: which note to play, when, for how long, at what velocity, on which instrument channel. The actual sound is generated by whatever synthesizer or soundfont library plays back the MIDI. This is why a MIDI file can be less than 50 KB but sound like a full orchestra. Converting MIDI to MP3 means rendering those instructions through a software synthesizer to produce actual audio, which can then be encoded as an MP3.
This converter renders your MIDI file using a built-in General MIDI soundfont directly in your browser via WebAssembly. The rendered audio is then encoded as MP3. No audio data is sent to a server. The quality of the output depends on the soundfont used; browser-based converters use standard GM soundfonts rather than high-end sample libraries, so the result is functional but not studio-quality.
Upload the MIDI file
Drop your .mid or .midi file onto the converter. Standard MIDI files (SMF Type 0 and Type 1) are both supported.
Preview the instruments
The converter displays the instrument channels in the MIDI file using the General MIDI program numbering (0-127). This tells you what instruments will sound in the render.
Render and encode
The WebAssembly synthesizer plays through the MIDI file using the built-in soundfont and records the output as raw audio, then encodes it to MP3 at the quality you select.
Download the MP3
Download the rendered MP3. If the instruments sound different from what you expected, the MIDI was likely authored for a specific soundfont or hardware synthesizer with different instrument samples.
Frequently asked questions
Why does the MIDI sound different from how I remember it?
MIDI playback quality depends entirely on the synthesizer and soundfont. An old Creative Sound Blaster card, a Roland GS module, a modern DAW with a high-end piano library, and a browser-based General MIDI soundfont all play the same MIDI file with different-sounding instruments. The browser converter uses a standard GM soundfont which may not match the author's intended sound.
How large is the resulting MP3 compared to the MIDI?
Dramatically larger. A MIDI file for a 4-minute song might be 30 to 100 KB. The equivalent MP3 at 128 kbps is about 4 MB. This is because the MP3 contains actual audio samples rather than just instructions.
Is the MIDI file uploaded to a server?
No. The synthesis and encoding run entirely in your browser using WebAssembly. Nothing is sent to any server.
Can I use the MP3 for music production or a sample library?
The output uses a General MIDI soundfont which produces serviceable but not professional-grade instrument samples. For production use, render the MIDI in a DAW with a high-quality virtual instrument library instead.
What is a soundfont?
A soundfont is a library of recorded audio samples for different instruments, stored in a format that a synthesizer can use to play back MIDI notes. General MIDI soundfonts cover 128 instrument programs and 46 percussion instruments as defined by the MIDI standard.