It's a great question and I don't have a clue who might be qualified to deal with it.

I do know that when I was a Peace Corps teacher in Ethiopia in the mid 1960's I was treated to some incredible singing from a trio of South African refugees who were resident at our school. I had never heard harmony singing with each individual being one note in a chord done so perfectly before. They were singing some of their revolutionary anthems. I was music director for a special event at the high school and contributed Pete Seeger renditions of "If I had a Hammer," "Kumbya," and "Which Side are You on." I do wish I hadn't lost my recording of what they sang, but it's long gone.

Charley Noble