Signal filters block or decrease (attenuate) unwanted frequencies or signal wave characteristics.

Active low pass filters pass signals from low frequencies and reject signals from high frequencies

Low pass filters pass signals from low frequencies and reject signals from high frequencies

Electromagnetic (EMI) filters and radio frequency interference (RFI) filters purify signals by attenuating the high-frequency RFI (typically 150kHz and up) and passing the low frequency EMI

RF filters and microwave filters are devices that pass or reject signals by frequency.

Active filters are electronic filers that use active components such as voltage amplifiers or operational amplifiers.

Long pass filters transmit a wide spectral band of long wavelength radiation while blocking short wavelength radiation.