New Fixed Frequency Band-Pass and Band-Reject (Notch) Filter modules Click below for more information on each product Frequency Devices introduces the "NEW" D64BP, D68BP and D68BR Series of 2- and 4-pole pair fixed center frequency (fo) filter modules. Each 32-pin DIP module is factory tuned to within 2% of the customer specified center frequency from 1 Hz to 100 kHz. Available "Q's" for band-pass modules are 1, 2, 5 or 10 and for band-reject modules 3 or 10.