What is the principle of filter?

Filter is an electronic circuit used to change the signal, which can change the frequency range of the signal, thus changing the characteristics of the signal. The principle of the filter is to change the characteristics of the signal by changing its frequency range. A filter can decompose a signal into multiple frequency bands, and then change the signal characteristics of each frequency band, thus changing the characteristics of the whole signal. Filters can be used to suppress or enhance signals in a specific frequency range, thus changing the characteristics of signals.