Timbres

Writing music that only has 4 chords, or one set chord progression, forces you to change something about it to keep it interesting.

But it can’t be the harmony.

The melody could change.

After hearing a piano playing the same four chords over and over it’ll get boring pretty quickly.

So you need to change timbres.

Change the instruments around. Move things between guitar and piano. Maybe have a synth. Alternate the timbres of the harmony parts and it’ll create a whole new sound that’ll keep those same four chords fresh.

This is often how producers do this with four chord loops. The chords stay the same, but the timbre changes drastically.

It can also be used to differentiate sections of a piece of music. The chorus could be staccato punches on piano and the verses could be a guitar finger picking the chords. Those two textures and timbres sound very different even if the chords stay the same.

ISJ