92 lines
2.4 KiB
C
92 lines
2.4 KiB
C
#include <stdlib.h>
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#include <math.h>
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#include <stdint.h>
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/* via http://www.rgba.org/articles/sfrand/sfrand.htm */
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static unsigned int mirand = 1;
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static float
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whitenoise() {
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union either {
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float f;
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unsigned int i;
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} white;
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mirand *= 16807;
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white.i = (mirand & 0x007FFFFF) | 0x40000000;
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return white.f - 3;
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}
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/* used to resemble https://github.com/swh/ladspa/blob/master/util/biquad.h */
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static void
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biquad_init(biquad *bq) {
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bq->x1 = bq->x2 = bq->y1 = bq->y2 = 0;
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}
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static biquad_interim
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design(double cw, double sw,
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double num0, double num1, double num2,
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double den0, double den1, double den2) {
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return (biquad_interim) {
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.b0 = num0* (1 + cw) + num1*sw + num2* (1 - cw),
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.b1 = num0*-2*(1 + cw) + num2*2*(1 - cw),
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.b2 = num0* (1 + cw) - num1*sw + num2* (1 - cw),
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.a0 = den0* (1 + cw) + den1*sw + den2* (1 - cw),
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.a1 = den0*-2*(1 + cw) + den2*2*(1 - cw),
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.a2 = den0* (1 + cw) - den1*sw + den2* (1 - cw),
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};
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}
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static biquad
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biquad_gen(filter_t type, double fc, double gain, double bw, double fs) {
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double w0, cw, sw, A, As, Q;
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w0 = ANGULAR_LIM(fc, fs);
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cw = cos(w0);
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sw = sin(w0);
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A = DB2LIN(gain/2);
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As = sqrt(A);
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Q = M_SQRT1_2*(1 - (w0/M_PI)*(w0/M_PI))/bw;
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/* skip = (fabs(A - 1) <= TINY); */
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biquad_interim bqi;
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#define d(n0,n1,n2,d0,d1,d2) bqi = design(cw,sw,n0,n1,n2,d0,d1,d2)
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switch (type) {
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case FILT_PEAKING: d(1, A/Q, 1, 1, 1/A/Q, 1); break;
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case FILT_LOWSHELF: d(1, As/Q, A, 1, 1/As/Q, 1/A); break;
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case FILT_HIGHSHELF: d(A, As/Q, 1, 1/A, 1/As/Q, 1); break;
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case FILT_LOWPASS: d(0, 0, 1, 1, 1/Q, 1); break;
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case FILT_HIGHPASS: d(1, 0, 0, 1, 1/Q, 1); break;
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case FILT_ALLPASS: d(1, -1/Q, 1, 1, 1/Q, 1); break;
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case FILT_BANDPASS: d(0, 1, 0, 1, 1/Q, 1); break;
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case FILT_BANDPASS_2: d(0, 1/Q, 0, 1, 1/Q, 1); break;
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case FILT_NOTCH: d(1, 0, 1, 1, 1/Q, 1); break;
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case FILT_GAIN: d(A, A, A, 1/A, 1/A, 1/A); break;
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}
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#undef d
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double a0r = 1/bqi.a0;
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biquad out;
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out.b0 = a0r*bqi.b0;
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out.b1 = a0r*bqi.b1;
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out.b2 = a0r*bqi.b2;
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out.a1 = -a0r*bqi.a1;
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out.a2 = -a0r*bqi.a2;
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return out;
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}
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static bq_t
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biquad_run(biquad *bq, bq_t x) {
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bq_t y;
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y = bq->b0*x + bq->b1*bq->x1 + bq->b2*bq->x2
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+ bq->a1*bq->y1 + bq->a2*bq->y2;
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bq->x2 = bq->x1;
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bq->x1 = x;
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bq->y2 = bq->y1;
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bq->y1 = y;
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return y;
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}
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