High harmony sits above the melody; low harmony sits below it. The obvious difference is range: if the tune sits in the middle of your voice, a third above may push you to your top and a sixth below to your bottom. The less obvious difference is what your ear has to do.

Above the tune, your line is the highest thing sounding and the ear naturally follows it, which makes it easier to hold and also easier to overdo. Below the tune, the melody is on top and the pull toward it is stronger, so the low part needs more independence.

The same notes, both ways

A third above and a sixth below are the same harmony note in different octaves. Play the third above, then the sixth below, and hear how the colour stays and the balance changes.

How to choose

• Go by range first. Sing the tune, then try both. The one that sits comfortably wins, because a strained harmony is a flat harmony.
• Learn the third above first anyway. Even if you will end up singing low, the third above teaches the shape of a harmony line in the easiest place to hear it. Then take it down an octave.
• In a group, take what is missing. If the room is full of high harmony, the low part is the one that makes the chord.