A pitch detector that shows the note you sing.

How the pitch detector works

Press Start and sing, hum or play a note. About sixty times a second the page takes the newest slice of sound from the microphone, finds how often its wave repeats, and turns that into a frequency and a note. The method is YIN, a pitch estimator published by Alain de Cheveigné and Hideki Kawahara in the Journal of the Acoustical Society of America in 2002 and widely used for voices. It looks for the shortest repeat in the wave, which keeps it from reading a note an octave low. Song Cage is a songwriting app for chords, lyrics and melody, and this is the same detector it uses when you sing a melody into a song.

The large note name is steadied over the last few readings so it holds still on a held note, while the needle and the cents figure follow every wobble. The piano roll shows the last six seconds: your voice is the solid line, and the note it is on lights up on the keyboard at the left. The roll follows your voice up and down, about two octaves at a time. Every note you hold for a quarter of a second joins the row along the bottom, so a tune you hum is written out as you go.

Nothing is recorded. Each slice of audio becomes a number and is thrown away, and the microphone switches off when you press Stop or leave the tab.

Sharp, flat and cents

A cent is a hundredth of a semitone: 100 cents from one piano key to the next, 1,200 in an octave. The meter shows how far your note sits from the nearest note on a piano tuned to A4 = 440 Hz. Right of centre is sharp, too high; left is flat, too low. Within 10 cents either side it reads In tune. Past 50 cents you are nearer the next note, and the note name changes.

Even a steady singer moves around the note. Vibrato swings the pitch above and below it several times a second, and the start of a note often scoops up from below. Judge a held note by where the needle settles, not by every flick. If you want to know whether you can land on a note you hear, the tone deaf test plays one and scores how close you sing it back.

Note frequencies

Each octave doubles the frequency, so A3 is 220 Hz, A4 is 440 Hz and A5 is 880 Hz. These are the notes the detector is most often asked about, from the guitar’s low E to a soprano’s high C.

Note frequencies with A4 tuned to 440 Hz

Note	Frequency	Where you meet it
E2	82.41 Hz	The lowest string on a guitar, near the bottom of a bass voice
A2	110.00 Hz	The guitar’s fifth string
C3	130.81 Hz	Low in a tenor’s range
A3	220.00 Hz	The A below middle C
C4	261.63 Hz	Middle C
A4	440.00 Hz	The note orchestras tune to
C5	523.25 Hz	The top of a tenor’s range, “tenor high C”
A5	880.00 Hz	High in a soprano’s range
C6	1,046.50 Hz	A soprano’s high C

What to use it for

• Check a held note. Sing a note and hold it. If the needle settles to one side, you know which way to move, and by how much.
• Write down a tune you hum. The row along the bottom is the melody, one note at a time. It shows the notes but not the rhythm; Song Cage’s melody capture writes both.
• Find the edges of your voice. Slide slowly from your lowest note to your highest and back. Gaps in the line show where your voice cracks or changes register. The vocal range test turns those two notes into a range, a voice type and the keys that fit.
• Tune a guitar roughly. Pluck a string and turn the peg until the cents figure is near zero. Standard tuning, from the lowest string: E2 (82.41 Hz), A2 (110.00 Hz), D3 (146.83 Hz), G3 (196.00 Hz), B3 (246.94 Hz), E4 (329.63 Hz).