Pole-zero pair, measurement

A plant has a second order pole near a second order zero, with the same Q, giving a peak near a notch for the module of the transfer function.
Since they are close to each other, the ratio of the peak and notch frequencies is bigger than the ratio of the pole and zero frequencies, and the maximum/minimum ratio is less than 2Q.
I have measured this frequency ratio and this extremum ratio. How can I compute the Q and the pole-zero frequency ratio ? Calculations look nasty:-(
Jean-Pierre Coulon (here "cacas.pam" is what others call "nospam")
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