Variable linear phase FIR filters

A class of linear-phase digital filters is discussed for which the filter coefficients are simple functions of the parameters determining the desired frequency response. In the case of lowpass filters, the 6-dB cutoff frequency is the parameter considered. High-pass, bandpass, bandstop, and notch filters can be obtained with simple transformations from a low-pass prototype. The filters are variable over nearly the whole frequency range from zero to half the sampling frequency. Due to direct control of filter coefficients, the length of the filter does not change when it is made variable