to control the frequency response in a read back circuit which is connected to a transducer retrieving magnetically recorded data it is a feature of the present invention in accordance with the last mentioned specific object to control such a frequency response in dependance upon the track diameter i e in response to a signal representing the diameter or radius or distance from the axis of rotation of the track from which data or information is being read and retrieved it is a feature of the present invention to cut and attenuate the frequency response of such a read back circuit in the higher frequency range and to a degree which increases with track diameter it is another feature of the present invention to boost the frequency response in such a read back circuit in the higher frequency range and to a degree which increases with a decrease in track diameter in accordance with the preferred embodiment of the present invention it is suggested to provide a filter circuit for connection to a transducer reading magnetically recorded data from annular tracks on a disk the filter operates in response to a signal which represents the track diameter and boosts higher frequency components of the reproduced signal for larger track diameters but cuts or attenuates the higher frequency components for smaller diameter tracks from.