Miriam Makeba, K. D. Lang and Nana Mouskouri are right up there, especially when it comes to range. Yma Sumac, too - at least 5 octaves, I think.

In bluegrass, Emmy Lou is great, but so are I Alison Krauss and Gillian Welch.

Moving farther away from bluegrass, I gotta mention an all-time favorite voice. The other day I heard a recording of a song from, probably, the 1940s, and I found myself thinking: "Who IS that? What an incredibly beautiful voice!" After awhile I recalled who it was: Ella Fitzgerald. She could range from soft cooing to belting it out and just had an exceptional tonal quality to her voice.

But seriously, how to you specify "the purest?"

And is "purest" necessarily "best?" Lots of folks prefer 'dirty voices' because they're more distinctive and interesting.

Genie