Electronic filter circuits: combinations of a capacitor (C) and an inductor (L) forming a simple high-pass filter (A) and low-pass filter (B).
An electronic filter is an arrangement of electronic components used in a circuit to transmit signals within a given frequency range, rejecting others. Electronic filters are used in radios, television receivers, telephone systems, etc.
A low-pass filter transmits frequencies below a specified cut-off and blocks out higher frequencies; typically it consists of an inductor in series with a capacitor shunted across the load to short out high-frequency current. In a high-pass filter the inductor and capacitor are interchanged and only high frequencies are transmitted. A bandpass filter blocks all frequencies outside two limits.