A filter is a circuit that separates some frequencies from others within mixed-frequency signals. It is used for preprocessing in measurement. The NF 3620 Series Dual Channel Programmable Filters are variable cut-off frequency filters as the cut-off frequency can be set to the required one. The 3620 Series have an extremely wide frequency range with cut-off frequency 0.01Hz to 1.59MHz for LPF, HPF, BPF and BEF (option). The use of the 3620 Series is not limited to electronics as it also covers a wide field of physical experiments, studies on physical properties and other related areas. Its attenuation slope is 24dB/Oct (3624/3627) and 48dB/Oct (3625/3628) and phase linear response is also available in the LPF mode.