Filters are essential components in many applications, from power supplies and audio electronics to radio communications and signal processing. A filter is a device or process that eliminates some unwanted components or characteristics from a signal. This can involve the complete or partial suppression of certain frequencies or frequency bands. Filtering is a type of signal processing, and it is not limited to the frequency domain.
In image processing, for example, filters can be used to eliminate correlations for certain frequency components while leaving others untouched. Filters are widely used in electronics and telecommunications, radio, television, audio recording, radar, control systems, music synthesis, image processing and computer graphics. They can be used to remove dust or dirt from air or gases, fluids, and electrical and optical phenomena. Air filters are used to clean the air, while electronic filters clean electrical signals from unwanted frequencies in the audio and intermediate ranges.
RF and microwave filters serve the same purpose but in the radio and microwave frequency range. EMI and RFI filters minimize or eliminate electromagnetic interference. Fluid filters remove debris from fluids, fuel filters remove contaminants from fuels, and hydraulic filters remove contaminants from hydraulic fluids. Water filters clean water for drinking and swimming as well as in water treatment plants.
Optical filters pass light and filter wavelengths of light. The various approaches to the ideal filter response are identified by names such as Butterworth, Chebyshev, Bessel, and others. The most commonly used filter is the Butterworth filter which has a planar maximum response in the passband. This means that passband flatness is the ideal emphasized filter characteristic but it comes at the expense of phase linearity and attenuation slope. The Butterworth filter has a good attenuation slope which makes it an excellent general purpose approach to the ideal filter when phase linearity is not important.
The Bessel filter is a linear filter with a maximum planar group delay (linear phase response) and is often used in audio flyover systems.
Air filterscome in many standard sizes so finding a fit is usually just a matter of length x width x height. Matching network design has much in common with filters and will often have filtering action as an incidental consequence. Butterworth filters are one of the most commonly used digital filters in motion analysis and audio circuits. Fluid filters capture less common forms of fluid filtration such as food, wine and spirits, natural gas, automotive oil, etc.
If this is not desirable then one of the members of the Gaussian family of filters can be used with the most common usually being called Bessel filter.