What does an app that tells you if you sing in tune actually measure?
A pitch app estimates the fundamental frequency of your voice many times a second and shows it against the nearest note, usually as a needle or a colour and a number of cents. That tells you whether a held note is sharp or flat. It does not tell you whether a phrase is musical, whether your breath will last, or whether the note you hit was the right one for the song unless it also knows the melody.
What the number means
A cent is one hundredth of a semitone. A reading of minus fifteen cents means you are fifteen hundredths of a semitone flat. Readings jump about on a real voice because pitch moves within a note, especially at the start of it and during vibrato, so look at where the needle settles rather than where it lands.
Two kinds of app
They look similar and answer different questions.
- A tuner shows the note you are on right now. Good for matching a played note and for checking a held tone. It has no idea what you meant to sing.
- A song-following app compares you with a known melody, so it can say you were flat on the third note of the line. That is the more useful judgement for learning a song, and it depends on the app knowing the song.
How to use one without chasing the needle
Sing the phrase first, then look. Watching the needle while you sing pulls your attention out of the sound and into the screen, and people start correcting mid-note, which teaches a scoop. Record, review, choose one note to fix, sing again.
Questions people ask
Do these apps work with a backing track playing?
Mostly not well. A pitch tracker fed two sources at once tends to lock onto the louder or the steadier, which may be the track. Practise the check on the voice alone, then sing with the track for feel.
Is a phone microphone good enough?
For pitch, yes. Phone microphones capture the fundamental of a voice cleanly at normal distance. Tone and loudness readings are less trustworthy on a phone; pitch is the robust one.