Your voice repeats a waveform pattern hundreds of times a second. The pitch tracker looks at short windows of audio, finds how often the pattern repeats, and converts that rate into a frequency. A clarity score says how confident it is. Breaths, consonants and room noise score low and are ignored.
The frequency is then measured against the nearest note in cents. There are 100 cents in a half step, so a reading of +20 means you are a little sharp of the note on screen. That is what the needle shows while you sing.
When you stop, a median filter smooths out brief jumps, and the curve is cut into notes wherever the pitch moves to a new half step and stays there for at least 80 milliseconds. A second pass with Basic Pitch then cleans up note starts and lengths.
Snap to key: fixing pitch without flattening the tune
Most people drift a little when they hum. A note meant as an E can land closer to an E♭, and a plain nearest-note rounding writes the wrong note. Snap to key solves that by allowing only the notes of the scale you pick.
If your melody is in G major, only G, A, B, C, D, E and F♯ are allowed. A hummed note that lands between F and F♯ is written as F♯, not F. The contour of the melody stays the same; only the out-of-key pitches move. If you are not sure which key you are in, check it with the Key Finder first.
Leave Snap to key off for blues, modal or chromatic lines where the “wrong” notes are on purpose. You can always drag single notes into place instead.
Hum, sing or whistle?
Humming gives the steadiest tone and the fewest surprises, which makes it a good default. Singing on a syllable like “da” adds a clear consonant at the start of each note, which helps when you sing fast repeated notes.
Singing the real lyrics works, but soft consonants and quick syllables can split one long note into two or merge two short ones. Whistling has a very clean tone but sits an octave or two above where you would sing the same tune, so plan to transpose it down.
From a hummed idea to a finished part
Once the melody is in MIDI, it is just notes. Drop the .mid into GarageBand, Logic Pro or Ableton Live and play it on any instrument. Quantize it to your song’s tempo if you want it tight; leave it loose if you want it to sound sung.
For a lead sheet, send the file to MIDI to Sheet Music. To hand the tune to a clarinet, sax or a singer with a different range, run it through Transpose Sheet Music. The melody you hummed on the bus becomes a part someone else can read.