Lowpass filters signficantly attenuate sinusoids above a certain “cutoff frequency” (), effectively only passing frequency components below the cutoff.
Highpass filters significantly attenuate sinusoids below a certain “cutoff frequency” and pass components higher than the cutoff.
The cutoff frequency of a filter is defined as the frequency at which the power transmitted is 1/2 the maximum power transmitted in the passband. This corresponds to a -3dB drop on a decibel scale. As the power of a signal is related to its amplitude squared, the cutoff frequency corresponds to a linear amplitude reduction of
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Bandpass filters only pass sinusoids above and below a certain frequency region.
Bandstop filters are designed to pass all sinusoids except those within a certain frequency region.
Resonance filters accentuate sinusoids within a certain frequency region. They may or may not pass sinusoidal frequencies outside that region.
Resonance filters are typically described in terms of their center frequency and quality factor (Q), which is given by the center frequency divided by the -3dB bandwidth. A higher indicates a “sharper” resonance.
Allpass filters do not affect the magnitude characteristics of a signal (their magnitude response is equal to 1 for all frequencies) but have frequency-dependent phase characteristics.