The invention relates to a circuit for a micromechanical structure-borne sound sensor and a method for operating said sensor, wherein voltages are applied by means of a voltage generator to at least one micromechanical element used for detecting structure-borne sound such that a change to the micromechanical element occurs. Furthermore, an evaluation circuit is provided which records and evaluates at least one electrically detectable parameter of the micromechanical element at a certain sampling rate. The at least one parameter is modified as a result of the change. A clock generator is also provided for generating the sampling rate and generating the cycle. A frequency generator is used for at least temporarily generating the cycle for the test operation, wherein the frequency generator generates the cycle as a multiple or as a factor of the sampling rate.