/* * Smoother * * Smoother is a one-pole smoothing filter, typically used on * control signals to create a "smootheramenteau" effect. * * This filter design uses the difference equation: * * y(n) = b0*x(n) - a1*y(n - 1) * * Where a1 is (0.5^(1/(t * sr))), and b0 is (1 - a1). * * More information on one-pole smoothers can be found here: * https://ccrma.stanford.edu/~jos/filters/One_Pole.html */  #include <math.h>#include <stdint.h>#include <stdlib.h> #include "soundpipe.h" int sp_smoother_create(sp_smoother **p){    *p = malloc(sizeof(sp_smoother));    return SP_OK;} int sp_smoother_destroy(sp_smoother **p){    free(*p);    return SP_OK;} int sp_smoother_init(sp_data *sp, sp_smoother *p){    p->y0 = 0;    p->b0 = 0;    p->a1 = 0;    p->psmooth = -100.0;    p->smooth = 0.01;     /* using this constant shaves off a multiply operation */    p->onedsr = 1.0/sp->sr;    return SP_OK;} int sp_smoother_compute(sp_data *sp, sp_smoother *p, SPFLOAT *in, SPFLOAT *out){    USED(sp);     if (p->psmooth != p->smooth) {        p->a1 = pow(0.5, p->onedsr/p->smooth);        p->b0 = 1.0 - p->a1;        p->psmooth = p->smooth;    }     p->y0 = p->b0 * (*in) + p->a1 * p->y0;    *out = p->y0;    return SP_OK;} int sp_smoother_reset(sp_data *sp, sp_smoother *p, SPFLOAT *in){    USED(sp);     p->y0 = *in;    return SP_OK;}