A melody is a sequence of moves in pitch, and there are only two kinds: to the neighbour, or a jump. The ratio between them decides how singable it is.
Break a melody down and all that remains is the distance to the next note. Near or far — that is the whole vocabulary.
Stepping to the neighbour
Moving to the next note of the scale. Easy to sing and easy to follow. Played in order it sounds like climbing stairs. Nursery rhymes and hymns are mostly this.
Leaping
Skipping notes to get to the next one. Memorable, and it creates lift. Do it repeatedly and the line becomes hard to sing and hard to follow. After a leap, a step in the other direction settles things again.
Moving to the neighbouring note is a step; skipping notes is a leap. Steps are singable, leaps stand out.
The mix depends on the instrument
Vocal melodies lean towards steps; guitar solos lean towards leaps. ChordMelo returns different results per mode because it changes exactly this ratio, along with the range.
- Vocal melody (mostly steps)
C | G | Am | F
- Guitar lead (more leaps)
C | G | Am | F
The guitar version spans much more vertical space and jumps around. The vocal one is gentler. Not better or worse — a voice and a fretboard simply reach different distances.
Generate a vocal melody and actually sing it. If you can sing it, it works.
Generate a vocal melodyLots of stepwise motion is easy to sing; a leap is memorable. After a leap, step back and it settles.