This hard nasal sustain with the intentional break at the end of the phrase was present (in a much softened form) in the Appalachian church music I heard in my childhood. Interestingly enough, if you watch any movie from the silver screen era, you'll hear the "traditional" Native American music sung like this. I wonder if there existed a real commonality, or if it was just Hollywood using a tonality its audience would perceive as rural? I can't help but wonder if the vocal style comes from the blaring sound of the pipes the tune may have once been played on.
I think that "nasal sustain" you're referring to is called "vocal feathering". Here is a definition I found: "A sudden or forceful raising of the soft palate against the back wall of the throat and/or a sudden closing of the glottis at the very end of a given note, generally accompanied by a rise in pitch" Your Native American theory is very interesting! I'll try and find some authentic Native American music that uses that feature. I've read somewhere that vocal feathering could also come from Germanic yodeling traditions.
@Danny Murphy I think there is also a lot of influence from Gaelic Psalm singing which is still sung in a few congregations in churches on the Hebrides Islands and I think a lot of the people who settled in the Appalachian region where of Scottish and Irish descent? I'm no expert but check this out: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-oPEa69nQGv0.html
My great aunt in North Georgia did that exact same thing on church. My mother did it on rarer occasion. As for the native American influence, I agree completely. There are no recordings of Major Ridge, Cherokee, but he was regarded as a great orator. They say the Cherokee stopped every 6 to 10 syllables to "grunt" much like the Appalchian preachers in the same area.
