ayu's voice is changing in this 10 years?

[prussian blue]

in AFSFXX her voice was totally like an innocent girl
and sometime it was annoying to me
because its high-pitched... well IMO
example: poker face

in i am and rainbow era her voice started to change into mature one
example: evolution, M

in memorial address and MY STORY era her voice is much stronger, she started to learn how to vibrato and she used very dolly sound~
example: CAROL, HONEY

but in M(U), secret and GUILTY her voice changed dramaticly... she almost use "shouting" and the vibrato is getting more frequece and sometime i'm quite annoyed wz that
example: MW (the yeah... yeah...), sotsugyou shashin in CDL

is it really ayu changed her voice? (naturally i mean)