/* * IIR filter * Copyright (c) 2008 Konstantin Shishkov * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /** * @file libavcodec/iirfilter.c * different IIR filters implementation */ #include "iirfilter.h" #include <math.h> /** * IIR filter global parameters */ typedef struct FFIIRFilterCoeffs{ int order; float gain; int *cx; float *cy; }FFIIRFilterCoeffs; /** * IIR filter state */ typedef struct FFIIRFilterState{ float x[1]; }FFIIRFilterState; /// maximum supported filter order #define MAXORDER 30 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type, enum IIRFilterMode filt_mode, int order, float cutoff_ratio, float stopband, float ripple) { int i, j; FFIIRFilterCoeffs *c; double wa; double p[MAXORDER + 1][2]; if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS) return NULL; if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0) return NULL; c = av_malloc(sizeof(FFIIRFilterCoeffs)); c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1)); c->cy = av_malloc(sizeof(c->cy[0]) * order); c->order = order; wa = 2 * tan(M_PI * 0.5 * cutoff_ratio); c->cx[0] = 1; for(i = 1; i < (order >> 1) + 1; i++) c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i; p[0][0] = 1.0; p[0][1] = 0.0; for(i = 1; i <= order; i++) p[i][0] = p[i][1] = 0.0; for(i = 0; i < order; i++){ double zp[2]; double th = (i + (order >> 1) + 0.5) * M_PI / order; double a_re, a_im, c_re, c_im; zp[0] = cos(th) * wa; zp[1] = sin(th) * wa; a_re = zp[0] + 2.0; c_re = zp[0] - 2.0; a_im = c_im = zp[1]; zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im); zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im); for(j = order; j >= 1; j--) { a_re = p[j][0]; a_im = p[j][1]; p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0]; p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1]; } a_re = p[0][0]*zp[0] - p[0][1]*zp[1]; p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0]; p[0][0] = a_re; } c->gain = p[order][0]; for(i = 0; i < order; i++){ c->gain += p[i][0]; c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) / (p[order][0] * p[order][0] + p[order][1] * p[order][1]); } c->gain /= 1 << order; return c; } av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order) { FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); return s; } #define FILTER(i0, i1, i2, i3) \ in = *src * c->gain \ + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \ res = (s->x[i0] + in )*1 \ + (s->x[i1] + s->x[i3])*4 \ + s->x[i2] *6; \ *dst = av_clip_int16(lrintf(res)); \ s->x[i0] = in; \ src += sstep; \ dst += dstep; \ void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep) { int i; if(c->order == 4){ for(i = 0; i < size; i += 4){ float in, res; FILTER(0, 1, 2, 3); FILTER(1, 2, 3, 0); FILTER(2, 3, 0, 1); FILTER(3, 0, 1, 2); } }else{ for(i = 0; i < size; i++){ int j; float in, res; in = *src * c->gain; for(j = 0; j < c->order; j++) in += c->cy[j] * s->x[j]; res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; for(j = 1; j < c->order >> 1; j++) res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; for(j = 0; j < c->order - 1; j++) s->x[j] = s->x[j + 1]; *dst = av_clip_int16(lrintf(res)); s->x[c->order - 1] = in; src += sstep; dst += sstep; } } } av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state) { av_free(state); } av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) { if(coeffs){ av_free(coeffs->cx); av_free(coeffs->cy); } av_free(coeffs); } #ifdef TEST #define FILT_ORDER 4 #define SIZE 1024 int main(void) { struct FFIIRFilterCoeffs *fcoeffs = NULL; struct FFIIRFilterState *fstate = NULL; float cutoff_coeff = 0.4; int16_t x[SIZE], y[SIZE]; int i; FILE* fd; fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH, FF_FILTER_MODE_LOWPASS, FILT_ORDER, cutoff_coeff, 0.0, 0.0); fstate = ff_iir_filter_init_state(FILT_ORDER); for (i = 0; i < SIZE; i++) { x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE)); } ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1); fd = fopen("in.bin", "w"); fwrite(x, sizeof(x[0]), SIZE, fd); fclose(fd); fd = fopen("out.bin", "w"); fwrite(y, sizeof(y[0]), SIZE, fd); fclose(fd); ff_iir_filter_free_coeffs(fcoeffs); ff_iir_filter_free_state(fstate); return 0; } #endif /* TEST */