An a cappella arrangement is a song for voices alone: a tune, and a few parts that harmonise with it. You don't need years of theory to make a simple one, just a handful of ideas and your ears.
Start with the melody
Everything is built around the tune. Choose a simple song you know well, with a clear tune and not too many chords, and put it in a key that suits whoever sings it. If the tune is uncomfortable, every other part suffers too.
Put a bass on the roots
Next, work out the chords under the tune. Many simple songs use only three: the home chord, and the chords built on the fourth and fifth notes of the scale. In the key of C, those are C, F and G.
Give the bass the root of each chord: the note the chord is named after. Under a C chord, the bass sings C. This gives the arrangement a firm floor, and it's the easiest bass part to sing. Later, you can let the bass step between roots now and then to make it walk.
Fill in the chord
A simple chord has three notes: the root, the third and the fifth. With a tune on top and a bass on the root, the alto and tenor share out what's left.
- Keep the third. It's the note that makes a chord sound major or minor, so have it in at least one part.
- Keep the upper parts close. The alto and tenor usually sit within an octave of the part above them.
- Don't let parts cross. Alto under the tune, tenor under the alto, bass at the bottom, so each line is easy to follow.
Keep every part singable
An arrangement can look fine on paper and be miserable to sing.
- Keep it in range. Roughly: soprano C4 to A5, alto G3 to D5, tenor C3 to A4, bass E2 to E4. Aim for the middle of each.
- Move by step, or hold. Inner parts that stay on a note or move to the next one up or down are easy to learn and blend well. Save big leaps for the tune or the bass.
- Sing each part yourself. If you can't sing it without effort, a beginner won't either.
A gentle note on one old rule: when two parts move together exactly a fifth or an octave apart (parallel fifths and octaves), they tend to blur into one. Don't worry much at first, but if a spot sounds hollow, that's often why.
Words or "oo"?
Backing parts don't have to sing the words.
- On "oo" or "ah": soft and blended, and the tune's words stay clear. A bass on "oo" is a lovely, simple start.
- On the words: fuller, more like a hymn, with everyone telling the story together.
Many arrangements mix the two, like the alto and tenor on the words and the bass on "oo".
Try it by ear
You can arrange without writing anything down. Record the tune, hum along a little below it (a third below is a good start), then add a low part on the roots. If it sounds good, it is good. An instrument can help you find the chords, but it's voices you're writing for.
Try it in Stackapella
Simple Gifts is a good model: the soprano sings the tune, the alto and tenor stay close beneath it on easy repeated notes, and the bass holds the roots on "oo". Learn a part or two to hear how it's built. Then choose Make your own:
- Sing it: paste the words and sing the tune line by line to a click. The app writes down the notes for you to check.
- Suggest them: the app makes alto, tenor and bass to fit your tune, in three styles, Simple, Warm and Bright. Hear each and pick one.
- If a chord isn't quite right, choose Try another chord there. If the tune and the bass move in parallel anywhere, the app names the bars.
- Or choose Write them and add the parts yourself in the note editor.
- Save it, then Record each part over the others, and hear your arrangement in your own voice.