Voice =F(Larynx, True vocal cord,C)

By now,
I distinguished my voice into

[chest voice][head voice][falsetto]

But actually I found out another relation seems more suitable.

Dependent Variance: Z=Voice
Independent Variance: Larynx(X), True vocal cord(Y)
Indifference number: C

F(a,b,C) = Z
F(a,b,C) = aX + bY + C