MIDI to MP3 Converter (MIDI Player)

MIDI files store notes, not sound: which key is pressed, when and how hard, and which instrument should play it. This converter reads a MIDI file in your browser and plays every note with built-in synthesized voices (piano, organ, guitar, bass, strings, brass, reeds, synths and a drum kit), then saves the result as an MP3 or WAV that any phone, car or video editor can play. You can change the tempo, transpose and choose one instrument for everything. The audio preview works as a simple MIDI player.

How to use this tool

1. Choose one or more .mid or .midi files (or tick "Play the demo song" to hear the voices first).
2. Optionally pick one instrument for every part, change the tempo or transpose.
3. Choose MP3 or WAV and press Calculate.
4. Play the result here and download it.

Formula

time (s) = ticks × tempo (µs per beat) ÷ 1,000,000 ÷ ticks per beat · frequency = 440 × 2^((note − 69) ÷ 12)

The parser reads Standard MIDI Files of type 0 and 1 (also .kar and .rmi): variable-length delta times, running status, tempo changes, time signatures, program changes, volume, expression, pan, sustain pedal and pitch bend (±2 semitones); volume, pan and pitch bend are taken as they are when each note starts, so slides and fades within a held note are not followed. Channel 10 is played as drums from the General MIDI percussion map. Each instrument family has its own voice built from a few harmonics with an envelope, so a piano note fades while an organ note holds. The song is mixed in stereo and its peak set to −1 dBFS. These are synthesized voices, not a General MIDI SoundFont, so expect a clean demo sound rather than realistic instruments.

Example

A MIDI file at 120 BPM with 480 ticks per beat that ends at tick 3,840 lasts 3,840 ÷ 480 = 8 beats × 0.5 s = 4.0 seconds. At a tempo of 50% it becomes 8.0 s. As a 192 kbps MP3, a 3-minute song is about 192,000 ÷ 8 × 180 = 4.3 MB, compared with a 20–60 KB MIDI file.