#define MAX_BANDS MAX_SPLITS + 1
typedef struct BiquadContext {
- double a0, a1, a2;
- double b1, b2;
+ double b0, b1, b2;
+ double a1, a2;
double z1, z2;
} BiquadContext;
static void set_lp(BiquadContext *b, double fc, double q, double sr)
{
- double thetac = 2.0 * M_PI * fc / sr;
- double d = 1.0 / q;
- double beta = 0.5 * (1.0 - (d / 2.0) * sin(thetac)) / (1.0 + (d / 2.0) * sin(thetac));
- double gamma = (0.5 + beta) * cos(thetac);
-
- b->a0 = (0.5 + beta - gamma) / 2.0;
- b->a1 = 0.5 + beta - gamma;
- b->a2 = b->a1 / 2.0;
- b->b1 = 2.0 * gamma;
- b->b2 = -2.0 * beta;
+ double omega = M_PI * fc / sr;
+ double cosine = cos(omega);
+ double alpha = sin(omega) / (2. * q);
+
+ double b0 = (1. - cosine) / 2.;
+ double b1 = 1. - cosine;
+ double b2 = (1. - cosine) / 2.;
+ double a0 = 1. + alpha;
+ double a1 = -2. * cosine;
+ double a2 = 1. - alpha;
+
+ b->b0 = b0 / a0;
+ b->b1 = b1 / a0;
+ b->b2 = b2 / a0;
+ b->a1 = -a1 / a0;
+ b->a2 = -a2 / a0;
}
static void set_hp(BiquadContext *b, double fc, double q, double sr)
{
- double thetac = 2.0 * M_PI * fc / sr;
- double d = 1.0 / q;
- double beta = 0.5 * (1.0 - (d / 2.0) * sin(thetac)) / (1.0 + (d / 2.0) * sin(thetac));
- double gamma = (0.5 + beta) * cos(thetac);
-
- b->a0 = (0.5 + beta + gamma) / 2.0;
- b->a1 = -(0.5 + beta + gamma);
- b->a2 = b->a0;
- b->b1 = 2.0 * gamma;
- b->b2 = -2.0 * beta;
+ double omega = M_PI * fc / sr;
+ double cosine = cos(omega);
+ double alpha = sin(omega) / (2. * q);
+
+ double b0 = (1. + cosine) / 2.;
+ double b1 = -1. - cosine;
+ double b2 = (1. + cosine) / 2.;
+ double a0 = 1. + alpha;
+ double a1 = -2. * cosine;
+ double a2 = 1. - alpha;
+
+ b->b0 = b0 / a0;
+ b->b1 = b1 / a0;
+ b->b2 = b2 / a0;
+ b->a1 = -a1 / a0;
+ b->a2 = -a2 / a0;
}
static void calc_q_factors(int order, double *q)
double *dst, const double *src,
int nb_samples)
{
- const double a0 = b->a0;
- const double a1 = b->a1;
- const double a2 = b->a2;
+ const double b0 = b->b0;
const double b1 = b->b1;
const double b2 = b->b2;
+ const double a1 = b->a1;
+ const double a2 = b->a2;
double z1 = b->z1;
double z2 = b->z2;
const double in = src[n];
double out;
- out = in * a0 + z1;
- z1 = a1 * in + z2 + b1 * out;
- z2 = a2 * in + b2 * out;
+ out = in * b0 + z1;
+ z1 = b1 * in + z2 + a1 * out;
+ z2 = b2 * in + a2 * out;
dst[n] = out;
}