Abstract: An apparatus and a method for detecting at least one periodically occurring defect on an object, in particular on a metal strip, in which at least one time signal is recorded from the moving object using a measuring method, the time signal is converted into a quality function using a stochastic method and one or more periodic signals in the time signal are inferred on the basis of this quality function in order to thereby detect at least one periodically occurring defect on the object. In order to obtain advantageous method properties, it is proposed to convert the time signal recorded by means of the measuring method, in particular the electromagnetic measuring method, into the quality function using a model-based estimation method, in particular using a maximum likelihood method.