Ear-training apps are built around a question: two notes play, and you say which interval it was. That is a real skill and it is not the singer's skill. A singer has to produce the interval: hear the first note, imagine the second, and land on it, usually while something else is sounding. You can be excellent at naming intervals and still miss a third above.

So ear training for singers should be hear-then-sing, and it should be graded, or you are training to feel right rather than to be right.

What to practise, in order

• Match a note. Hear it, sing it back. Boring and essential.
• Hold a note against a moving line. The drone exercises. This is where singers differ from instrumentalists: the pull of another line is the whole difficulty.
• Sing a fixed interval against a line. A third above, all the way through a tune. Then a sixth below, a fifth, a fourth. Each one is a different colour and a different pull.
• Sing by ear, no staff. Hear the tune and the key, and find the line yourself. This is the actual goal and it should arrive last, once the intervals are in your voice.

Hear one interval against a line

A fifth above, all the way through. Open and hollow rather than sweet, and easy to mistake for the tune because neither voice sounds like the lead. Solo it, sing it, then bring the tune back.

Being graded

Blend is this list, as lessons: drones, then each interval in turn, on tunes ordered from stepwise to leaping, with the staff withdrawn as you improve and every note marked as you sing it. The first stages are free and need no account.