exceptional voices of female singers (non-classical)

Should add that Celine Rudolph is German jazz singer based in France who has training in African and Brazilian music in addition to jazz. Check out her legant vocals on her album with remarkably talented jazz guitarist Lionel Louke titled Obsessions. The music is beautiful, intimate, and playful.

Maria Bethania is a singer, a mega-star, from Brazil; her music spans styles from samba to bossa nova to jazz. Check out Santa Barbara, the first track from her 2009 album Encanteria. Gorgeous vocals. Beautifully recorded.

G

Aziz Ali, Gillian Welch.......

Great question., most surveys by highly regarded voice coaches consider Karen Carpenter the finest contralto voice ever recorded. Just released complete set of new vinyl albums.  Feb 4 will be 35 years since she died.   

These are the only ones I've heard who belong in the top tier of "as close to vocally pure as possible".

Ann Wilson
I saw her in concert in her prime and when she sang Dream of the Archer it just sent chills through me. She lost it by the late 80's.

Oceans of Slumber's Cammi Gilbert
Check out their song Sunlight (Live) on Youtube, or their new song The Banished Heart
(caution: Metal, but I think most can handle it. It's mild.)

Bonnie Raitt
I don't know why her voice sounds so much better on ballads, but her rendition of I Can't Make You Love Me is stunning. Adele attempted this song and butchered it. Only Bonnie can pull it off.

Whitney Houston
Celine Dion
Not my style, but I appreciate their stunning talent.

@toolshedamps

Aziz Ali, Gillian Welch.......

Do you mean Azam Ali?  If so, +1