heterophony

In heterophony, there is only one melody, but different variations of it are being sung or played at the same time.

Heterophony can be heard in the Bluegrass, "mountain music," Cajun, and Zydeco traditions.

You can also try simply searching for "heterophony" at YouTube or other sites with large collections of recordings.

This heterophony is, in fact, a good thing.

The two-hour concert was a roaring heterophony, street-music jams that incorporated, and were improved by, the small disjunctions among its drummers and singers.