Turn a hum into an instrument part

Hum, sing, or whistle a melody into your phone, and ferraus turns it into a MIDI part played by a real instrument sound. This walkthrough shows the one-step command, then the steps underneath it so you can fix wrong notes. Outputs are trimmed copies of what ferraus 0.1.0 printed.

You need: a recording of one melody line (idea.wav): humming, "la la la", whistling, or a single instrument. Record somewhere quiet, close to the microphone, one note at a time. No downloads are needed.

Making a test file. Without a recording, render a melody with a soft lead sound and roll off its brightness so it behaves roughly like a hum (melody.mid is any one-line MIDI melody; see Make a score for how to write one from JSON):

ferraus render melody.mid --instrument builtin:lead --tail 0.5s -o lead.wav
ferraus fx lead.wav -o idea.wav --fx "lowpass:freq=900Hz" --fx "tremolo:rate=5.5,depth=15%" --channels 1

1. One step: hum to piano

ferraus hum idea.wav --to piano -o idea-piano.wav --json

{"ok": true, "command": "hum",
 "outputs": [{"path": "idea-piano.mid", "role": "midi"}, {"path": "idea-piano.wav", "duration_s": 11.77}],
 "params": {"bpm": "99.84 (audio)", "grid": "1/16", "strength": "80%", "key": "A minor (confidence 0.91; snapped)", "to": "piano", ...},
 "metrics": {"notes": 11, "tempo_confidence": 1.0, "mean_note_confidence": 0.995},
 "result": {"mode": "mono", "engine": "pyin", "bpm": 99.84, "key": "A minor", "pitch_range": ["A4", "E5"],
            "midi": "idea-piano.mid", "audio": "idea-piano.wav", "instrument": "piano", ...}}

ferraus tracked the pitch, found the tempo (99.84 BPM; the melody was played at 100) and the key, split the line into notes, nudged them 80% of the way onto a sixteenth-note grid, and played them with a piano. It also wrote the MIDI part, idea-piano.mid, so you can edit or re-voice it.

Listen for: the right notes in the right order, and the rhythm of your hum (not a machine-straight version of it, unless you asked for that).

2. Missing notes? Split repeated notes

Our test melody has 16 notes but ferraus found 11. The missing ones are repeated notes: when you hum the same pitch twice without a clear break, it sounds like one long note. --onset-sensitivity controls how readily a note is split on a small dip in level or pitch:

ferraus transcribe idea.wav -o idea.mid                            # 11 notes (default 50%)
ferraus transcribe idea.wav --onset-sensitivity 90% -o idea90.mid  # 13 notes
ferraus transcribe idea.wav --onset-sensitivity 100% -o idea100.mid

The note lists, from each .notes.json file:

50%:  E5 D5 C5 D5 E5 C5 B4 A4 B4 C5 A4
90%:  E5 D5 C5 D5 E5 E5 C5 B4 A4 B4 C5 A4 A4
100%: E5 D5 C5 D5 E5 E5 E5 C5 C5 B4 A4 B4 C5 C5 A4 A4    (all 16)

hum takes the same flag: ferraus hum idea.wav --to piano --onset-sensitivity 100% -o idea-piano.wav. Going the other way, if a wobbly hum is split into extra short notes, lower the sensitivity or raise --min-note 120ms. Humming each note on "da" or "ta" instead of "mm" gives the clearest onsets of all.

3. Check every note

transcribe writes a JSON list beside the MIDI file with a confidence for every note:

ferraus transcribe idea.wav -o idea.mid --json

{"ok": true, "command": "transcribe",
 "outputs": [{"path": "idea.mid"}, {"path": "idea.notes.json", "role": "notes"}],
 "result": {"mode": "mono", "notes": 11, "bpm": 99.84, "key": "A minor", "key_confidence": 0.91,
            "key_snapped": true, "notes_snapped": 0, "pitch_range": ["A4", "E5"], "mean_confidence": 0.995, ...}}

{"start_s": 0.01, "end_s": 0.6197, "pitch": 76, "name": "E5", "velocity": 92, "confidence": 0.993, ...}

Notes with low confidence are the ones to listen to. Out-of-key notes are moved to the nearest note of the key when the key confidence is above 0.6 (--key-snap off keeps them).

4. Choose the instrument, tempo, and feel

ferraus hum idea.wav --to strings --grid 1/8 --strength 100% --bpm 100 -o idea-strings.wav
ferraus hum bass-idea.wav --to "Acoustic Bass" --bpm 92 -o bass.wav
  • --to takes any instrument name render understands: piano, strings, a General MIDI name such as "Acoustic Bass" or "Flute", gm:48, an installed sound, or a plugin (plugin:"Surge XT"). With no sounds installed, a built-in synth plays it; install the free General MIDI sound bank for much better instruments: ferraus sounds install gm-basic -y (31 MB).
  • --grid 1/8 --strength 100% snaps fully to eighth notes (tight and mechanical); --grid off keeps your timing exactly.
  • --bpm fixes the tempo instead of detecting it, so the part lines up with a song at that tempo.
  • --octave auto (the default) moves the part into the instrument's comfortable range, so a hummed bass line plays in the bass register.

5. Re-voice the MIDI without re-humming

ferraus render idea-piano.mid --instrument "Acoustic Bass" -o idea-bass.wav
ferraus midi transpose idea-piano.mid --semitones -12 -o idea-low.mid
ferraus midi quantize idea-piano.mid --grid 1/8 --strength 100% -o idea-tight.mid

Any DAW can open the .mid files too.

Reference

hum · transcribe · render · midi quantize · midi transpose · sounds install