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avfilter/af_acrossover: simplify coefficients

This commit is contained in:
Paul B Mahol 2020-11-26 11:53:17 +01:00
parent cc74700a83
commit 4e3c4dfbf3
1 changed files with 38 additions and 26 deletions
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64
libavfilter/af_acrossover.c
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@ -39,8 +39,8 @@
#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;
@ -146,30 +146,42 @@ static av_cold int init(AVFilterContext *ctx)
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);
double omega = M_PI * fc / sr;
double cosine = cos(omega);
double alpha = sin(omega) / (2. * q);
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 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);
double omega = M_PI * fc / sr;
double cosine = cos(omega);
double alpha = sin(omega) / (2. * q);
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 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)
@ -250,11 +262,11 @@ static void biquad_process(BiquadContext *b,
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;
@ -262,9 +274,9 @@ static void biquad_process(BiquadContext *b,
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;
}