Patent US 3,958,213

An adaptive gain control for a signal processor of an intrusion detection system comprises a circuit which utilizes the weighted summation of selected characteristics of sensed signals for producing optimum control of the gain of the circuit for discriminating between target and non-target signals more effectively. The parameters of signal envelope, envelope amplitude variance and signal frequency obtained from a processor such as that described in U.S. Pat. No. 3,696,369 are fed to a summing amplifier through resistors having weighted values calculated from previously recorded seismic signals obtained from several previously identified sites which, taken as a group, are representative of the type or types of sites in which the detection system is to be installed. The output of this summing amplifier is a control signal which is applied to a controlled instrumentality such as an amplifier or attenuator for optimizing signal level and thus enabling better circuit discrimination between target and non-target signals at a particular site. This invention further comprehends a method of processing signals for optimizing discrimination between desired and undesired signals by deriving selected signal parameters of signal envelope, amplitude variance and frequency, conditioning those parameters by assigning weights to them in accordance with data derived from prerecorded signals taken from sites representative of intended system installation and classified as target or non-target signals, summing these conditioned signal parameters in a summing amplifier to derive a control signal and applying the control signal to a controlled instrumentality which varies the gain of the circuit for optimizing identification of target signals and rejection of non-target signals.