The invention relates to a calibration unit (20) for an audio system (2) having a generator (4) for generating a pilot tone (6), and a detector (16a-c) for the pilot tone (6), wherein at least one parameter (P1, 2) determining the pilot tone (6) is changeable, which calibration unit comprises an input unit (22) for optionally setting the parameter (P1, 2), wherein for at least one value (W1, 2) of the parameter (P1, 2), all detectors indicate a detection of the pilot tone (6). An audio system (2) comprises said calibration unit (20). In a method for operating the calibration unit (20), the parameters (p1, 2) is regulated in such a way that all detectors (16a-c) indicate a detection of the pilot tone (6). A computer program carries out all steps of the method, when the program is performed on a computer and/or the calibration unit (20) or the audio system (2).