9. The common ratio of the geometric sequence $a+\log _{2} 3, a+\log _{4} 3, a+\log _{8} 3$ is $\qquad$ .
$$
q=\frac{a+\log _{4} 3}{a+\log _{2} 3}=\frac{a+\log _{8} 3}{a+\log _{4} 3}=\frac{\log _{4} 3-\log _{8} 3}{\log _{2} 3-\log _{4} 3}=\frac{\frac{1}{2}-\frac{1}{3}}{1-\frac{1}{2}}=\frac{1}{3} .
$$