A MIDI file is a list of notes, not a recording, so it has to be played by instruments before it can become an MP3. This converter performs your .mid file with General MIDI SoundFont samples, lets you swap instruments, change the tempo, transpose and add reverb, then saves the result as an MP3 or WAV.
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Instruments
Preview each part, swap its instrument or mute it before rendering.
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How it works: MIDI files contain notes, not sound. This page reads the notes, plays them through General MIDI instrument samples (the FluidR3 GM SoundFont, downloaded per instrument from a public CDN) or a built-in synthesizer, renders the mix faster than real time with the Web Audio API, adds reverb, and encodes the result with the LAME MP3 encoder. Your file is never uploaded.
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How to use the MIDI to MP3
Open a MIDI file: drop a .mid file on the box or click Choose MIDI file. A demo (Bach's Minuet in G) is loaded so you can try it right away.
Check the instruments: press ▶ Preview on a part to hear it, choose a different General MIDI instrument, or tick Mute.
Adjust tempo, transpose and reverb to taste, and pick the MP3 bitrate (192 kbps is plenty for most music).
Press Convert to MP3. Instrument samples download the first time, then the song renders faster than real time.
Listen and download: play the result in the page, then press Download MP3 (or Download WAV for lossless audio).
General MIDI numbers its 128 melodic programs in 16 families of 8. The instrument menu on each part uses this list; channel 10 is always the drum kit.
Programs
Family
Programs
Family
1–8
Piano
65–72
Reed (saxophones, oboe, clarinet)
9–16
Chromatic percussion
73–80
Pipe (flutes, recorder, ocarina)
17–24
Organ
81–88
Synth lead
25–32
Guitar
89–96
Synth pad
33–40
Bass
97–104
Synth effects
41–48
Strings
105–112
Ethnic
49–56
Ensemble (string sections, choir)
113–120
Percussive
57–64
Brass
121–128
Sound effects
Tempo and transposition math
MIDI stores tempo as microseconds per quarter note, so BPM = 60,000,000 ÷ tempo value (500,000 µs = 120 BPM). Setting the tempo slider to 150% divides every note time by 1.5, so a 3:00 song becomes 2:00. Transposing by n semitones multiplies each pitch by 2n/12: +12 is one octave up, +7 a perfect fifth, -2 a whole step down.
Tips for good-sounding renders
Files from notation software (MuseScore, Sibelius, Finale) often have every note at the same velocity. A little reverb (20 to 35%) makes them sound far less mechanical.
Muddy mix? Lower the reverb or choose Room, and try muting doubled parts.
Piano-only pieces sound best with the Acoustic Grand Piano and a concert hall setting around 25%.
Need just one instrument's line? Mute all other parts and render, then trim the result with an audio cutter.
Frequently asked questions
How do I convert MIDI to MP3?
Open your .mid file, keep or change the instruments, and press Convert to MP3. The page plays every note through SoundFont instrument samples using the Web Audio API, mixes the parts with reverb, and encodes the result with the LAME MP3 encoder, all inside your browser.
Why does a MIDI file sound different in every program?
MIDI only stores which notes to play, when, how hard and on which instrument number. The actual sound comes from whatever synthesizer or SoundFont plays it, so the same file sounds different on Windows, a keyboard or this converter. Here it uses the FluidR3 General MIDI SoundFont.
What is a SoundFont?
A SoundFont is a bank of recorded instrument samples mapped to the 128 General MIDI programs plus a drum kit. FluidR3 GM is a widely used free SoundFont (MIT licence) by Frank Wen. This tool loads its samples one instrument at a time, only for the instruments your song uses.
Can I change the tempo or key before converting?
Yes. The tempo slider scales the speed from 50% to 200% (or type an exact BPM), and Transpose shifts all pitched notes by up to 12 semitones up or down. Drums are never transposed. Tempo changes stored in the file are kept in proportion.
Can I make a backing track by removing the melody?
Yes. Tick Mute on any part, for example the melody or vocal line, and only the remaining parts are rendered. You can also replace an instrument, such as turning a piano part into strings.
Does it work without an internet connection?
Choose Built-in synthesizer to render with oscillator-based instruments that need no download. The SoundFont samples and the MP3 encoder are fetched from public CDNs the first time; if the encoder cannot load, you can still download a WAV file.
Are drums supported?
Yes. Notes on MIDI channel 10 are played as the General MIDI drum kit (kick, snare, hi-hats, toms, cymbals and percussion) using a built-in drum synthesizer, so drum tracks always render even without downloads.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.