A method and apparatus for a frequency shift keying (FSK) demodulator use a configuration to improve the autocorrelation for better receiver performance. The demodulator uses parallel first and second lines connected to the same input signal, the first line having a delay element to provide an integer-delay of M, the second parallel line having a filter for causing a group delay of .tau.+M where .tau. is fractional, and a multiplier for receiving the signals from said first and second lines and generating a resultant signal from which a base band signal can be recovered. The resultant signal is passed through a low pass base band filter to recover the base band signal. .tau. may have a value of 3.25 and M may be 6. The demodulator may selectively be implemented in caller ID service and in low end modems chosen from a group comprising V.21, Bell 103, V.23 and Bell 202A modems.