The invention is a method of characterizing the frequency response of the servo control system in a disk drive having a sampled servo system having a sampling rate and a nominal bandwidth, wherein the sampled servo system comprises a plant and a servo controller that controls the plant using a compensator and a gain element with a nominal open loop gain. The invention is, in more detail, a method for adaptively modifying the servo controller to compensate for plant variations which are incompatible with the nominal gain and bandwidth, including the steps of implementing a self-generated bode plot to determine a gain margin and a phase margin, and if the gain margin is not greater than a predetermined minimum, adjusting the open loop gain of the servo controller to provide a gain margin which is greater than the predetermined minimum at a bandwidth which is different than the nominal bandwidth; and adjusting the compensator to provide a phase margin which is greater than a predetermined minimum.