public static void calculate_filter1_coefficients(discrete_base_node node, double fc, double type, ref discrete_filter_coeff coeff)
{
double den;
double wc;
double two_over_T;
/* calculate digital filter coefficents */
/*wc = 2.0*M_PI*fc; no pre-warping */
wc = node.sample_rate() * 2.0 * tan(M_PI * fc / node.sample_rate()); /* pre-warping */
two_over_T = 2.0 * node.sample_rate();
den = wc + two_over_T;
coeff.a1 = (wc - two_over_T) / den;
if (type == DISC_FILTER_LOWPASS)
{
coeff.b0 = coeff.b1 = wc / den;
}
else if (type == DISC_FILTER_HIGHPASS)
{
coeff.b0 = two_over_T / den;
coeff.b1 = -(coeff.b0);
}
else
{
/* FIXME: reenable */
//node->m_device->discrete_log("calculate_filter1_coefficients() - Invalid filter type for 1st order filter.");
}
}
public static void calculate_filter2_coefficients(discrete_base_node node, double fc, double d, double type, ref discrete_filter_coeff coeff)
{
double w; /* cutoff freq, in radians/sec */
double w_squared;
double den; /* temp variable */
double two_over_T = 2 * node.sample_rate();
double two_over_T_squared = two_over_T * two_over_T;
/* calculate digital filter coefficents */
/*w = 2.0*M_PI*fc; no pre-warping */
w = node.sample_rate() * 2.0 * Math.Tan(Math.PI * fc / node.sample_rate()); /* pre-warping */
w_squared = w * w;
den = two_over_T_squared + d * w * two_over_T + w_squared;
coeff.a1 = 2.0 * (-two_over_T_squared + w_squared) / den;
coeff.a2 = (two_over_T_squared - d * w * two_over_T + w_squared) / den;
if (type == global_object.DISC_FILTER_LOWPASS)
{
coeff.b0 = coeff.b2 = w_squared / den;
coeff.b1 = 2.0 * (coeff.b0);
}
else if (type == global_object.DISC_FILTER_BANDPASS)
{
coeff.b0 = d * w * two_over_T / den;
coeff.b1 = 0.0;
coeff.b2 = -(coeff.b0);
}
else if (type == global_object.DISC_FILTER_HIGHPASS)
{
coeff.b0 = coeff.b2 = two_over_T_squared / den;
coeff.b1 = -2.0 * (coeff.b0);
}
else
{
/* FIXME: reenable */
//node->device->discrete_log("calculate_filter2_coefficients() - Invalid filter type for 2nd order filter.");
}
}
