The usual advice is “record yourself singing the melody, then sing the harmony over it.” That is right, and it is also most of what a duet partner gives you: a tune that keeps going whether or not you are on your note. The rest of what a partner gives you, someone to tell you when you are off, is the part solo practice usually lacks.

Three things to sing against

• A recording of yourself. Sing the tune, play it back, sing the harmony over it. Blending with your own voice is unusually good training, because the two lines have the same timbre and any gap between them is pitch, not tone.
• A played melody. A piano or a synth line. Cleaner than a voice, easier to hear against, less like the real thing.
• A drone. One held note, and you sing scales and lines over it. The best exercise there is for learning to stay put.

How to know whether you got it

Record the pair and listen back. If you can hear which line is which, and the two never land on the same note by accident, you are close. If you cannot hear whether you were flat on the long notes, that is the limit of listening back: our own voice is the hardest one to judge.

This is the part Blend was built for. Half its clips are duets with yourself: you sing the tune, it records you, and you sing the harmony over your own take while your microphone grades every note. The reveal plays both of your voices together.