Bandpass filters pass the selected range or band of frequencies (without distorting the input signal) that can be either narrow or wide, attenuating all those outside of this range. In other words, a frequency selective filter known as Band Pass Filter (BPF). The bandwidth of the filter is the difference between the upper and lower cutoff frequency points of two filters. BNDP556 bandpass filter is a pair of frequency cutoff state-variable filters, designed to adjust the audio frequency bandwidth. The filters are 3-Slope (18 dB/oct), designed for Butterworth response. The cutoff frequencies are tunable. The Low-end cutoff filter can be adjusted to a frequency in the range from 20 Hz to 200 Hz. The High-end cutoff filter can be adjusted to a frequency in the range from 2 kHz to 20 kHz. The ideal bandpass filter would have a completely flat response (all frequencies would be passed to the output without amplification or attenuation, and would completely attenuate all frequencies outside the passband). In practice, bandpass filters are not ideal. There is a region outside of the intended passband where frequencies are attenuated, but not rejected. This is a filter roll-off (stop-band) before and after the bandpass range.