A self-biased magnetoresistive reproduce head is excited with an a.c. sense current which simultaneously a.c. biases the magnetoresistive element. When reproducing a pre-recorded signal, the spectrum of the head output includes sidebands containing the signal information associated with a suppressed carrier at twice the bias frequency. These sidebands are far removed in the head output frequency spectrum from sources of low frequency noise. The invention teaches demodulating these sidebands by means of a locally generated carrier corresponding to the suppressed carrier which has a frequency of twice the bias frequency. This locally generated carrier is coherent with the bias frequency source. The information signal is thereby recovered in a portion of the spectrum immune from the effects of low frequency interfering noise.