Most unusual/mesmerizing female voice.

Yma Sumac, unusual for sure and one for the ages.

I have never heard any human being approach what she does with her voice. The range is absolutely spellbounding. Now it is another issue altogether whether her voice could be considered mesmerizing.

My personal favorite is Sarah Vaughn, the great contralto. She is both unusual and at her best mesmerizing. While Billie Holiday and Ella Fitzsgerald, both contemporaries get more of the accolades I feel there is more emotion in her performances simply because of her vocal range which is the greatest among jazz singers. Her pitch is absolutely perfect and she can get into the bass range of male singers which is most unusual among female vocalists. While her voice got deeper as she got older she never lost the emotion she could evoke in her performances. Billie Holiday I feel is a favorite because of her vulnerability which the Divine One didn't convey to the same degree and is therefore more appealing to more. I get that for sure.

I am really surprised she hasn't been mentioned till now. I'm sorry, but some of the above choices are real lightweights in comparison. Check out Sarah Vaughn.

How about Ema Sumac, the "Peruvian Princess" who's heyday was primarily in the 50's when she was an international star with a 4-5 octave range. Whether you consider her voice mesmerizing or not, she is/was to her many fans. One thing for sure though her unique voice has got to rank up there with anyone in the unusual category. Then you factor in her beauty which makes watching her, whether a fan or not, much easier.