Ideal Filters 2.6 2001/06/14 2002/06/10 Richard G. Baraniuk richb@rice.edu Justin Romberg jrom@rice.edu Richard G. Baraniuk richb@rice.edu Michael Haag mjhaag@rice.edu allpass bandpass bandstop filter fourier transform frequency domain highpass lowpass signals systems Describes five ideal filters. There are four fundamental filters. They are Lowpass -- blocks high frequencies, allowing low frequencies through Highpass -- blocks low frequencies, allowing high frequencies through Bandpass -- blocks all frequencies except those within a certain range Bandstop -- blocks only the frequencies within a certain range, allowing all others to pass through

Lowpass Highpass Bandpass Bandstop Ideal frequency domain representations of the four fundamental filters.

Another term one may come across in the study of filters is an "allpass" filter. This is one that allows all frequencies through. The only meaningful effect an allpass filter can have is on the phase of the signal.