The Model 34A is a dual filter with two identical channels covering a tunable frequency range from 3Hz to 2MHz. Each channel can function independently with either low-pass or high-pass response at 24dB/octave attenuation or connected in series in the same mode to provide 48dB/octave attenuation. Band-pass or band-reject operation at 24dB/octave can be obtained. Either maximally flat (Butterworth) response or linear phase (Bessel) operation for pulse signal filtering is selectable. Both input and output amplifiers provide either 0dB or 20dB of gain. The Model 34A is a plug-in filter card which is operational only when inserted in the five-card Model 3905A/3905B/3905C or the sixteen-card Model 3916A/3916B/3916C Mainframe. Each Mainframe includes a microprocessor plug-in card; the Model 39A-05 for the 3905A/3905B/3905C, and the 39A-16 for the 3916A/3916B/3916C. The filter and microprocessor cards are easily accessible from the rear of the Mainframe. The filer is controlled by the Mainframe which provides local/IEEE-488 programming, displays for the input and output gain, cutoff frequency and channel selection. Non-volatile, battery- backed, CMOS memory permits the storing and recalling of 85 selectable groups in the 3905A/3905B/3905C and 25 in the 3916A/3916B/3916C. Storing and recalling group settings is accomplished with only one command. Self-testing of the digital circuitry occurs upon power-up.