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filter_jz.cpp
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filter_jz.cpp
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/***** filter.cpp *****/
#include <filter_jz.h>
Filter::Filter() {
//Do nothing.
}
Filter::Filter(int filterType_, float cutoffFrequency_, float T) {
filterType = filterType_;
cutoffFrequency = cutoffFrequency_;
calculate_coefficients(T);
}
// Calculate filter coefficients given a T. (Usually 1/sampleRate)
void Filter::calculate_coefficients(float T)
{
//Do the pre-warping here.
float w = (2/T)*atan(M_PI*cutoffFrequency*T);
// Could make this variable in the future?
float q = 1/sqrt(2);
switch(filterType) {
case FILTER_TYPE_LOW_PASS:
//LPF coefficients:
a_0 = 1 + (2/(w*q*T)) + (4/(w*w*T*T));
a_1 = 2 - (8/(w*w*T*T));
a_2 = 1 - (2/(w*q*T)) + (4/(w*w*T*T));
b_0 = 1;
b_1 = 2;
b_2 = 1;
break;
case FILTER_TYPE_BAND_PASS:
//BPF coefficients:
a_0 = (4/(T*T)) + ((2*w)/(q*T)) + (w*w);
a_1 = (2*w*w) - (8/(T*T));
a_2 = (4/(T*T)) - ((2*w)/(q*T)) + (w*w);
b_0 = (2*w)/(q*T);
b_1 = 0;
b_2 = -(2*w)/(q*T);
break;
case FILTER_TYPE_HIGH_PASS:
//HPF coefficients:
a_0 = (4/(T*T)) + ((2*w)/(q*T)) + (w*w);
a_1 = (2*w*w) - (8/(T*T));
a_2 = (4/(T*T)) - ((2*w)/(q*T)) + (w*w);
b_0 = 4/(T*T);
b_1 = -8/(T*T);
b_2 = 4/(T*T);
break;
}
}
float Filter::processNew(float x_) {
// Process new input
x0 = x_;
y0 = ((x0*b_0 + x1*b_1 + x2*b_2) - (y1*a_1 + y2*a_2))/a_0;
// Update the filter state for the next time we come through processNew
x2 = x1;
x1 = x0;
y2 = y1;
y1 = y0;
return y0;
}
Filter::~Filter() {
//Do nothing here.
}