Abstract: The demodulator is especially adapted for a data signal (F'c) that was recorded on tape in the form of a frequency modulated signal together with a reference signal (F'R) of frequency greater than the greatest frequency of the data signal, so that both signals are subject to the same proportional frequency errors. During each cycle of the data signal, a representation of the period of one cycle of the reference signal is measured and stored. Then at the end of each following cycle of the data signal, there is produced a pulse of area dependent on the representation. A filter (LPF) produces a signal representing the area of each pulse averaged over one cycle of the data signal.