What this conversion does
AAC is compressed sound; MIDI is a list of notes. Going from AAC to MIDI means transcribing the recording: finding each note's pitch, start, length and loudness. The page uses basic-pitch, an open-source model developed by Spotify, which analyses the audio locally in your browser. The model files download once, and your AAC file is not uploaded.
AAC recordings often come from phones, video downloads and screen captures. A typical case is a melody you played on a piano app, a song you sang into a messaging app, or a tune from a video you want to learn. Transcription turns that sound into notes you can edit, print as sheet music or play with another instrument.
What to expect
- Strong results: solo piano, solo guitar, a single voice, whistling, a flute or violin line.
- Reasonable results: a melody with light accompaniment. The model is polyphonic and finds chords, but some notes will be missing or extra.
- Weak results: full pop or rock mixes with drums, bass and many layers.
- No results for drums: percussion has no clear pitch and is not written as MIDI notes.
Melody-only mode is useful for songs: it keeps the most prominent line and drops accompaniment notes.
The effect of AAC compression
AAC at 128 kbps or more usually transcribes almost as well as an uncompressed file. Low-bitrate AAC, and especially HE-AAC from internet radio or voice apps at 32 to 64 kbps, rebuilds high frequencies artificially. This can confuse the model and create short false notes in the upper range. If you have a higher-quality copy, use that. Reducing background noise first with noise reduction also helps with phone recordings.
Using the result
The MIDI file has no sound of its own; open it in a DAW, a notation program or a keyboard app and choose the instrument you like. Timing follows the recording exactly, so quantize the notes if you need clean notation. For audio files in other formats, see MP3 to MIDI, and to turn MIDI back into sound, use the MIDI converter.