The electrical circuits known as filter manufacturers , which change an electrical signal dependent on the frequency in the amplitude and phase. This unwanted signal components are attenuated and suppressed.

Known applications are:

     * Radio / Radio: Selection of a specific frequency to receive a station. Only the frequency is received. All other frequencies are filtered out.
     * speakers (crossover): The different frequencies for treble, bass and midrange to be split and distributed to the appropriate speakers.
     * Power Filter: Suppress clicks when you turn the other customers and other disorders

Filter in the classical sense, such as low-or high-pass, change the frequency response. They are also called filter circuit. Circuits and methods change, the more complex properties such as phase angle, impedance and noise components, are also under the term filter. In audio engineering, digital and analog frequency filter (filter) also known as an equalizer (EQ ​​short). This includes presence filter, filter absence, band pass filters, high pass and low pass.