fandaal

Any waveform can be decomposed into a set of sine waves of
various frequencies and phases, and the waveform can be reconstructed
by simply summing these sine waves together. Filters are
usually described in terms of their ability to suppress or pass
various different frequencies. The most common types of filters
are: (1) low-pass filters, which attenuate high frequencies and pass
low frequencies; (2) high-pass filters, which attenuate low frequencies
and pass high frequencies; (3) bandpass filters, which attenuate
both high and low frequencies, passing only an intermediate
range of frequencies; and (4) notch filters, which attenuate some
narrow band of frequencies and pass everything else.