ref: 264e4718c21792ed8ee230d39aa2b9ac88d73b14
dir: /modules/diode.c/
/*
* Diode
*
* Based on Will Pirkle's Diode Ladder filter design.
* Code adapted from the CCRMA Chugin WPDiodeLadder
*
*/
#include <stdlib.h>
#include <math.h>
#include "soundpipe.h"
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
int sp_diode_create(sp_diode **p)
{
*p = malloc(sizeof(sp_diode));
return SP_OK;
}
int sp_diode_destroy(sp_diode **p)
{
free(*p);
return SP_OK;
}
static SPFLOAT sp_diode_opva_fdbk_out(sp_data *sp, sp_diode *p, int filt)
{
return p->opva_beta[filt] *
(p->opva_z1[filt] + p->opva_fdbk[filt] * p->opva_delta[filt]);
}
static SPFLOAT sp_diode_opva_compute(sp_data *sp, sp_diode *p, SPFLOAT in, int filt)
{
/*
double x_in = (xn*m_dGamma + m_dFeedback + m_dEpsilon*getFeedbackOutput());
double vn = (m_da0*x_in - m_dZ1)*m_dAlpha;
double out = vn + m_dZ1;
m_dZ1 = vn + out;
*/
/* m_dBeta*(m_dZ1 + m_dFeedback*m_dDelta); */
SPFLOAT x_in = (in*p->opva_gamma[filt]
+ p->opva_fdbk[filt]
+ p->opva_eps[filt] * sp_diode_opva_fdbk_out(sp, p, filt));
SPFLOAT vn = (p->opva_a0[filt]*x_in -
p->opva_z1[filt])*p->opva_alpha[filt];
SPFLOAT out = vn + p->opva_z1[filt];
p->opva_z1[filt] = vn + out;
return out;
}
static void sp_diode_update(sp_data *sp, sp_diode *p)
{
/* calculate alphas */
SPFLOAT G1, G2, G3, G4;
SPFLOAT wd = 2*M_PI*p->freq;
SPFLOAT T = 1/(SPFLOAT)sp->sr;
SPFLOAT wa = (2/T)*tan(wd*T/2);
SPFLOAT g = wa*T/2;
int i;
/* Big G's */
G4 = 0.5*g/(1.0 + g);
G3 = 0.5*g/(1.0 + g - 0.5*g*G4);
G2 = 0.5*g/(1.0 + g - 0.5*g*G3);
G1 = g/(1.0 + g - g*G2);
/* big G value gamma */
p->gamma = G4*G3*G2*G1;
p->SG[0] = G4*G3*G2;
p->SG[1] = G4*G3;
p->SG[2] = G4;
p->SG[3] = 1.0;
/* set alphas */
for (i = 0; i < 4; i++) p->opva_alpha[i] = g/(1.0 + g);
/* set betas */
p->opva_beta[0] = 1.0/(1.0 + g - g*G2);
p->opva_beta[1] = 1.0/(1.0 + g - 0.5*g*G3);
p->opva_beta[2] = 1.0/(1.0 + g - 0.5*g*G4);
p->opva_beta[3] = 1.0/(1.0 + g);
/* set gammas */
p->opva_gamma[0] = 1.0 + G1*G2;
p->opva_gamma[1] = 1.0 + G2*G3;
p->opva_gamma[2] = 1.0 + G3*G4;
/* set deltas */
p->opva_delta[0] = g;
p->opva_delta[1] = 0.5*g;
p->opva_delta[2] = 0.5*g;
/* set epsilons */
p->opva_eps[0] = G2;
p->opva_eps[1] = G3;
p->opva_eps[2] = G4;
}
int sp_diode_init(sp_data *sp, sp_diode *p)
{
int i;
/* initialize the 4 one-pole VA filters */
for (i = 0; i < 4; i++) {
p->opva_alpha[i] = 1.0;
p->opva_beta[i] = -1.0;
p->opva_gamma[i] = 1.0;
p->opva_delta[i] = 0.0;
p->opva_eps[i] = 1.0;
p->opva_fdbk[i] = 0.0;
p->opva_a0[i] = 1.0;
p->opva_z1[i] = 0.0;
p->SG[i] = 0.0;
}
p->gamma = 0.0;
p->K = 0.0;
/* Filter coeffs that are constant */
/* set a0s */
p->opva_a0[0] = 1.0;
p->opva_a0[1] = 0.5;
p->opva_a0[2] = 0.5;
p->opva_a0[3] = 0.5;
/* last LPF has no feedback path */
p->opva_gamma[3] = 1.0;
p->opva_delta[3] = 0.0;
p->opva_eps[3] = 0.0;
p->opva_fdbk[3] = 0.0;
/* default cutoff to 1000hz */
p->freq = 1000;
p->res = 0;
/* update filter coefs */
sp_diode_update(sp, p);
return SP_OK;
}
int sp_diode_compute(sp_data *sp, sp_diode *p, SPFLOAT *in, SPFLOAT *out)
{
int i;
SPFLOAT sigma;
SPFLOAT un;
SPFLOAT tmp = 0.0;
/* update filter coefficients */
p->K = p->res * 17;
sp_diode_update(sp, p);
p->opva_fdbk[2] = sp_diode_opva_fdbk_out(sp, p, 3);
p->opva_fdbk[1] = sp_diode_opva_fdbk_out(sp, p, 2);
p->opva_fdbk[0] = sp_diode_opva_fdbk_out(sp, p, 1);
sigma =
p->SG[0] * sp_diode_opva_fdbk_out(sp, p, 0) +
p->SG[1] * sp_diode_opva_fdbk_out(sp, p, 1) +
p->SG[2] * sp_diode_opva_fdbk_out(sp, p, 2) +
p->SG[3] * sp_diode_opva_fdbk_out(sp, p, 3);
un = (*in - p->K * sigma) / (1 + p->K * p->gamma);
tmp = un;
for (i = 0; i < 4; i++) {
tmp = sp_diode_opva_compute(sp, p, tmp, i);
}
*out = tmp;
return SP_OK;
}