Butterworth Filter

The examples provided here use this signal:

$\sin(10\pi t) + \sin(30\pi t) + \sin(60\pi t)$

Butterworth Filter

Low-Pass Filter

The parameters for this filter are as follows:

• Order ⇨ 4
• Cutoff Frequency ⇨ 9Hz
• Sampling Frequency ⇨ 100Hz

Code

int Fs = 100; //Sampling Frequency in Hz  
int order = 4; //order of the filter  
int cutOff = 9; //Cut-off Frequency  
Butterworth flt = new Butterworth(Fs); //signal is of type double[]  
double[] result = flt.lowPassFilter(signal, order, cutOff); //get the result after filtering  

High-Pass Filter

The parameters for this filter are as follows:

• Order ⇨ 4
• Cutoff Frequency ⇨ 29Hz
• Sampling Frequency ⇨ 100Hz

Code

int Fs = 100; //Sampling Frequency in Hz  
int order = 4; //order of the filter  
int cutOff = 29; //Cut-off Frequency  
Butterworth flt = new Butterworth(Fs); //signal is of type double[]  
double[] result = flt.highPassFilter(signal, order, cutOff); //get the result after filtering  

Band-Pass Filter

The parameters for this filter are as follows:

• Order ⇨ 4
• Lower Cutoff Frequency ⇨ 12Hz
• Upper Cutoff Frequency ⇨ 18Hz
• Sampling Frequency ⇨ 100Hz

Code

int Fs = 100; //Sampling Frequency in Hz  
int order = 4; //order of the filter  
int lowCutOff = 12; //Lower Cut-off Frequency  
int highCutOff = 18; //Higher Cut-off Frequency  
Butterworth flt = new Butterworth(Fs); //signal is of type double[]  
double[] result = flt.bandPassFilter(signal, order, lowCutOff, highCutOff); //get the result after filtering  

Band-Stop Filter

The parameters for this filter are as follows:

• Order ⇨ 4
• Lower Cutoff Frequency ⇨ 7Hz
• Upper Cutoff Frequency ⇨ 28Hz
• Sampling Frequency ⇨ 100Hz

Code

int Fs = 100; //Sampling Frequency in Hz  
int order = 4; //order of the filter  
int lowCutOff = 7; //Lower Cut-off Frequency  
int highCutOff = 28; //Higher Cut-off Frequency  
Butterworth flt = new Butterworth(Fs); //signal is of type double[]  
double[] result = flt.bandStopFilter(signal, order, lowCutOff, highCutOff); //get the result after filtering