ref: 264e4718c21792ed8ee230d39aa2b9ac88d73b14
dir: /modules/smoother.c/
/* * 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) { 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) { p->y0 = *in; return SP_OK; }