ction = new LowpassFilterButterworthSection ( double cutoffFrequencyHz, int numSections, double Fs) Public LowpassFilterButterworthImplementation Protected LowpassFilterButterworthSection section Public class LowpassFilterButterworthImplementation Then call the compute() method on the object repeatedly, passing in an input sample and receiving a filtered sample as the return value. To use the LowpassFilterButterworthImplementation, HighpassFilterButterworthImplementation, or BandpassFilterButterworthImplementation, construct the object with the desired cutoff frequency or frequencies, number of 2-pole sections, and the sample frequency (Fs). BandpassFilterButterworthImplementation.cs.HighpassFilterButterworthImplementation.cs.

LowpassFilterButterworthImplementation.cs.The code includes an implementation of an n th-order FIR filter for the zero (numerator) polynomials and an implementation of an n th-order IIR filter for the pole (denominator) polynomials. A bandpass filter is implemented as a cascade of a lowpass and a highpass filter. In the code, the lowpass and highpass filters are implemented according to the coefficient derivation from the design document. Then a substitution of variable s=1/s transforms the lowpass filter into a highpass filter, and the bilinear z-transform is used to derive the coefficients of the equivalent highpass digital filter. The design starts with a continuous-time lowpass Butterworth filter and uses the bilinear z-transform to derive the coefficients of the equivalent digital filter. BackgroundĪ Word document giving the filter design via bilinear z-transformation is included. This is a C# implementation of digital lowpass, highpass, and bandpass Butterworth filters of arbitrary order (n cascaded 2-pole sections). Download Butterworth_Filter_Design.zip - 17.5 KB.

Low pass filter image processing c