A Signal Filter is a passive component, which allows specific frequency bands to pass and reject other electrical signals, mainly for noise reduction. The design integrates multilayer ceramic capacitors, inductors, dielectric resonators and crystals.

The Filter finds use in circuits of audio equipment, video equipment, broadband and communication. Electronic signal processing filter is described to be linear or non-linear, analogue or digital, shift invariance, passive or active circuit.

The filter frequency response can be classified as:

• high-pass
• low-pass
• band-pass
• band-stop
• notch
• all-pass filter
• cut-off frequency.

The order of a filter refers to the slope of the transition to roll-off around the cut-off frequency. A first-order filter responds at -6 dB per octave, a second-order filter decreases at -12 dB, a third-order at -18 dB, on a logarithmic scale. The analogue filter in a linear design of a network synthesis type is known as the Butterworth filter, Chebyshev filter, Elliptic filter, Bessel filter and Gaussian filter.