Abstract: Embodiment illustrates technique for better controlling "head spacing" i.e., spacing of a magnetic transducer from the recording surface of a moving medium, such as a magnetic disk -- this involving impressing signals on the recording surface (along a given track) at two prescribed frequencies, so that, upon detection of this signal, one frequency will be attenuated discriminatorily more than the other at all "erroneous" head spacings whereby a "null-seeking" servo control and associated head elevation system may be monitored to maintain optimum head spacing, (e.g., where two frequencies detected at same amplitude). Better control of head/medium spacing in non-contact magnetic recording systems is achieved, especially where one signal is a very high frequency signal which is significantly attenuated whenever there is significant spacing error, while it is readily detected at the proper spacing; while the other signal is relatively unaffected by head spacing.