Filter (electronics)

electronic circuit that removes unwanted components from the signal, or enhances wanted ones, or both

Electronic filters are electrical circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both. Electronic filters can be:

Frequency response of hi-pass filter
low-pass filter.

The most common types of electronic filters are linear filters, regardless of other aspects of their design. Digital filters use a Fourier transform.