An audio filter is typically designed to pass some frequency regions through unattenuated while significantly attenutating others. In some applications, such as in the design of graphic equalizers or CD players, the filters are designed according to a set of objective criteria such as pass band, pass band attenutation, stop band and stop band attenutation, where the pass bands are the frequency ranges for which audio is attenuated less than a specified maximum, and the stop bands are the frequency ranges for which the audio must be attenuated by a specified minimum.
In other applications, such as with synthesizers or sound effects, the aesthetic of the filter must be evaluated subjectively.
Audio filters can be implemented in analog circuitry as analog filters or in DSP code as digital filters.
See also: electronic filter