Louise,
I don't agree at all on what you assess as a
female voice. I've got at least 1000 jazz
and blues songs (most of them bought!!)
in mp3 form and none sound like what your advocating!!
Listen to Fitzgerald, Vauguan or dozens of others
and tell me they sound as you states.
Their notes are purer and more simple
at the start of their carreer, but 5-10 years later in their heyday,
their voice is rich in higher harmonics which give a very
particular sound to the voice (and its their signature).
Maybe your thinking of Diana Krall, which I like, but has
kind of a weak voice which is heavily amplified and post treated
(she didn't start as a singer).
Even Norah Jones as a heavy timbre
to her voice which is different than what your saying.
Plenty of pop singer too have voices with heavy timbre, Sheryl Crow,
Nelly Furtado, Anastacia. All those voice are chock full of harmonics, Sheryl Crows voice is way lower than mine.
Considering the amount of vibrato and bluesy modulation, I'd
be surprised a young kid could do this, but if they can, hey that's fine.
But, anyway, a child male or women before puberty have voices that are
just about equivalent. The pitch and the resonnance is the same.
After that, the voice breaks and its much lower than what I did here.
The average fundamental frequency for the passage is in the middle of the soprano range, with top notes going over F5 (that's in the top soprano). Because its done in a bluesy way with modulation you don't feel the height as much a with a pure note.
I'm not saying I've got nothing to work on.
But, knowing I was going for chock middle
of the jazz voice and that's what I'm going for.
Applying such correction wouldn't make sense.
To conclude, the voice has to match the style your going for.
If you want breathy, I can sing in a Dido (very breathy and light) way
or Chantal Kraviatchuk way (purer voice but with some timbre)
Most breathy singer have almost no voices too speak of and are heavily amplified (example, Britney, and hundreds of others). Breathy is
a bad way to sing in general and is not sustainable without
amplification. I heard Dido's voice on a live radio program and
she does have a pretty good voice even if it is breathy.