Abstract: A filter which uses both an analog portion and a digital portion to optimize the filter performance. A simple analog filter provides a rough filtering of the input signal. The output of the analog filter is converted into digital form and supplied to a digital filter. The coefficients of the digital filter are changed by a digital computer in order to correct for the errors in the filtered signal produced by the analog filter. The coefficients necessary for the digital filter to provide an error offset are determined by comparing the filtered value of a test signal through the analog filter to an ideal filtered value of such test signal.