An automatic control system is disclosed herewith which causes the notch ter incorporated in a sonar system or any other appropriate utilization apparatus to be electrically by-passed in response to a predetermined minimum doppler present within a data signal being filtered thereby. It includes such uniquely combined elements as envelope detectors, rate-of-decay and rate-of-rise amplifiers, bistable multivibrators, an inverter, and an AND gate for adjusting the position of a selector switch connected for alternately electrically by-passing the notch filter. In addition, the gain of a variable gain amplifier disposed within an automatic gain control loop that includes the aforesaid elements and notch filter may be optionally employed to regulate the gain of the data signal supplied to said notch filter in correspondence with the by-passed and non-by-passed conditions thereof.