[B_coeffs, A_coeffs ] = butter(4, 100/(16000/2), 'high');
state = zeros( 4, 1 );
input = zeros( 64,1 );
for i=1:64
input(i)=i;
end
[filtered_output, state] = filter( B_coeffs, A_coeffs, input, state );
int main(...
{
for(int test=0; test<64;test++)
Xin[test]=test+1;
...
high_pass_filter_init(...
high_pass_filter_do(...
}
// Do the filtering
void high_pass_filter_do( t_high_pass_filter* hpf, float *Xin, float *Yout )
{
double Xi, Yi;
double z0 = hpf->state[0],
z1 = hpf->state[1],
z2 = hpf->state[2],
z3 = hpf->state[3];
unsigned int N = 64;
unsigned int i = 0;
for(i=0;i<N;i++)
{
Xi = Xin[i];
Yi = hpf->B_coeffs[0] * Xi + z0;
z0 = hpf->B_coeffs[1] * Xi + z1 - hpf->A_coeffs[1] * Yi;
z1 = hpf->B_coeffs[2] * Xi + z2 - hpf->A_coeffs[2] * Yi;
z2 = hpf->B_coeffs[3] * Xi + z3 - hpf->A_coeffs[3] * Yi;
z3 = hpf->B_coeffs[4] * Xi - hpf->A_coeffs[4] * Yi;
Yout[i] = (float) Yi;
}
hpf->state[0] = z0;
hpf->state[1] = z1;
hpf->state[2] = z2;
hpf->state[3] = z3;
return;
}
// Filter struct
typedef struct
{
float A_coeffs[5];
float B_coeffs[5];
float state[4];
} t_high_pass_filter;
// Create filter
void high_pass_filter_init( t_high_pass_filter* hpf)
{
hpf->A_coeffs[0] = 1.0000;
hpf->A_coeffs[1] = -3.8974;
hpf->A_coeffs[2] = 5.6974;
hpf->A_coeffs[3] = -3.7025;
hpf->A_coeffs[4] = 0.9025;
hpf->B_coeffs[0] = 0.9500;
hpf->B_coeffs[1] = -3.7999;
hpf->B_coeffs[2] = 5.6999;
hpf->B_coeffs[3] = -3.7999;
hpf->B_coeffs[4] = 0.9500;
hpf->state[0] = 0.0;
hpf->state[1] = 0.0;
hpf->state[2] = 0.0;
hpf->state[3] = 0.0;
}
