The Models 3320, 3321, 3322 and 3323 Filters illustrated in Figure 1, are variable, electronic Filters with digitally tuned cutoff frequencies". The Models 3320 and 3322 have a cutoff frequency range from 0, 001 Hz to 99. 9 kHz. The Models 3321 and 3323 are tunable over the range from 0, 01 Hz to 99. 9 kHz. The pass-band gain is unity (Odb) or 10 (20db), with attenuation rates of 24db per octave outside the pass-band. Maximum attenuation is greater than 80db and the output hum and noise is less than 500 microvolts. The Model 3320 (Model 3321) can function as either a High-Pass or Low-Pass Filter, In the High-Pass mode of operation the maximum input signal is plus or minus 7 volts peak in the Odb gain position, plus or minus 0. 7 volts peak in the 20db gain position, and the upper 3db point occurs at approximately 1 MHz. In the Low-Pass mode the Filter is direct-coupled and the combined ac plus dc input signal should not exceed ±1 volts peak in the Odb gain position and ±0. 7 volts peak in the 20db gain position. The Model 3322 (Model 3323) consists of two of the Model 3320 (Model 332 1) mounted in a single cabinet isolated from each other, with independent power supplies and input and output connectors. When these two filter channels are switched to the same mode of operation and cascaded, with both channels set to the same cutoff frequency, the Model 3322 (Model 3323) will function as a High-Pass or Low- Pass Filter with an attenuation rate of 48db per octave. If the two channels are connected in series, and one channel is operated in the Low-Pass mode and the other channel in the High-Pass mode, the Model 3322 (Model 3323) will function as a Band-Pass Filter with an attenuation rate of 24db per octave outside the pass-band. W'hen the two channels are connected in parallel, as described in Section 2.3, the Model 3322 (Model 3323) will function as either a Band-Reject Filter with cutoff frequency limits from 0. 00 1 Hz to 99.9 kHz (0.01 Hz to 99.9 kHz - Model 3323) or provide a null at any frequency between 0. 01 Hz and 10 kHz (0. 1 Hz and 10 kHz - Model 3323). The Filter has a maximally flat (Butterworth) characteristic when the FUNCTION switch(s) is in the Low-Pass MAX FLAT position. For pulse-type wave-forms this switch should be in the Low-Pass RC (Low Q) position, optimum for transient-free filtering.