The state space form of the SVF [1][2][3] consists of the following system of differential equations $$\begin{array}{rcl} \dot{s_1}(t) &=& - \omega [ 2 \zeta s_1(t) + s_2(t) + i(t) ] \\ \dot{s_2}(t) &=& \omega s_1(t) \\ \end{array}$$ corresponding to a system matrix $$A = \matrix{ - 2 \zeta \omega & -\omega \\ \omega & 0}.$$ Here $2\zeta=1/Q$ with $Q$ the usual pole--based definition of \emph{quality factor}, and $\omega = 2\pi f$ the angular frequency. Personally, I prefer to use the parameter $\zeta$ over $Q$ as it makes the expression of the poles a bit easier to read. The pole equation $$p(z) = \det(A-Is) = s^2 + 2 \zeta \omega s + \omega^2 = 0$$ has two solutions $$s_\pm = \omega (- \zeta \pm \sqrt{\zeta^2 - 1}).$$ If $\zeta < 1$ the poles are complex conjugate with complex angle only dependent on $\zeta$, i.e. unit norm phase component $e^\theta = \zeta+i\sqrt{1-\zeta^2}$ where $\cos\theta = \zeta$. % [1] http://www.earlevel.com/main/2003/03/02/the-digital-state-variable-filter/ % [2] entry://20130319-224319 % [3] http://en.wikipedia.org/wiki/State_variable_filter