The transfer function of a magnetic mirror plasma containing a feedback loop is measured experimentally. The measurements are obtained in a configuration where 1) the interchange mode is weakly damped, and 2) the interchange mode is unstable, but stabilized by the feedback loop. The results are in good agreement with the theoretically derived transfer function involving parameters (e.g. damping rates) determined by fitting the theoretical curve to the data. This method of analysis has diagnostic utility for mode identification and the measurement of damping rates.