3 * Copyright (c) 2008 Konstantin Shishkov
5 * This file is part of FFmpeg.
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 * different IIR filters implementation
27 #include "iirfilter.h"
29 #include "libavutil/common.h"
32 * IIR filter global parameters
34 typedef struct FFIIRFilterCoeffs{
44 typedef struct FFIIRFilterState{
48 /// maximum supported filter order
51 static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
52 enum IIRFilterMode filt_mode,
53 int order, float cutoff_ratio,
58 double p[MAXORDER + 1][2];
60 if (filt_mode != FF_FILTER_MODE_LOWPASS) {
61 av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
62 "low-pass filter mode\n");
66 av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
67 "even filter orders\n");
71 wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
74 for(i = 1; i < (order >> 1) + 1; i++)
75 c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
79 for(i = 1; i <= order; i++)
80 p[i][0] = p[i][1] = 0.0;
81 for(i = 0; i < order; i++){
83 double th = (i + (order >> 1) + 0.5) * M_PI / order;
84 double a_re, a_im, c_re, c_im;
91 zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
92 zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
94 for(j = order; j >= 1; j--)
98 p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
99 p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
101 a_re = p[0][0]*zp[0] - p[0][1]*zp[1];
102 p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
105 c->gain = p[order][0];
106 for(i = 0; i < order; i++){
108 c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
109 (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
111 c->gain /= 1 << order;
116 static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
117 enum IIRFilterMode filt_mode, int order,
118 float cutoff_ratio, float stopband)
120 double cos_w0, sin_w0;
123 if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
124 filt_mode != FF_FILTER_MODE_LOWPASS) {
125 av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
126 "high-pass and low-pass filter modes\n");
130 av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
134 cos_w0 = cos(M_PI * cutoff_ratio);
135 sin_w0 = sin(M_PI * cutoff_ratio);
137 a0 = 1.0 + (sin_w0 / 2.0);
139 if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
140 c->gain = ((1.0 + cos_w0) / 2.0) / a0;
141 x0 = ((1.0 + cos_w0) / 2.0) / a0;
142 x1 = (-(1.0 + cos_w0)) / a0;
143 } else { // FF_FILTER_MODE_LOWPASS
144 c->gain = ((1.0 - cos_w0) / 2.0) / a0;
145 x0 = ((1.0 - cos_w0) / 2.0) / a0;
146 x1 = (1.0 - cos_w0) / a0;
148 c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0;
149 c->cy[1] = (2.0 * cos_w0) / a0;
151 // divide by gain to make the x coeffs integers.
152 // during filtering, the delay state will include the gain multiplication
153 c->cx[0] = lrintf(x0 / c->gain);
154 c->cx[1] = lrintf(x1 / c->gain);
159 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
160 enum IIRFilterType filt_type,
161 enum IIRFilterMode filt_mode,
162 int order, float cutoff_ratio,
163 float stopband, float ripple)
165 FFIIRFilterCoeffs *c;
168 if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
171 FF_ALLOCZ_OR_GOTO(avc, c, sizeof(FFIIRFilterCoeffs),
173 FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
175 FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
180 case FF_FILTER_TYPE_BUTTERWORTH:
181 ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
184 case FF_FILTER_TYPE_BIQUAD:
185 ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
189 av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
197 ff_iir_filter_free_coeffs(c);
201 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
203 FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
207 #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
209 #define CONV_FLT(dest, source) dest = source;
211 #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt) \
212 in = *src0 * c->gain \
213 + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \
214 + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
215 res = (s->x[i0] + in )*1 \
216 + (s->x[i1] + s->x[i3])*4 \
218 CONV_##fmt(*dst0, res) \
223 #define FILTER_BW_O4(type, fmt) { \
225 const type *src0 = src; \
227 for (i = 0; i < size; i += 4) { \
229 FILTER_BW_O4_1(0, 1, 2, 3, fmt); \
230 FILTER_BW_O4_1(1, 2, 3, 0, fmt); \
231 FILTER_BW_O4_1(2, 3, 0, 1, fmt); \
232 FILTER_BW_O4_1(3, 0, 1, 2, fmt); \
236 #define FILTER_DIRECT_FORM_II(type, fmt) { \
238 const type *src0 = src; \
240 for (i = 0; i < size; i++) { \
243 in = *src0 * c->gain; \
244 for(j = 0; j < c->order; j++) \
245 in += c->cy[j] * s->x[j]; \
246 res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; \
247 for(j = 1; j < c->order >> 1; j++) \
248 res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; \
249 for(j = 0; j < c->order - 1; j++) \
250 s->x[j] = s->x[j + 1]; \
251 CONV_##fmt(*dst0, res) \
252 s->x[c->order - 1] = in; \
258 #define FILTER_O2(type, fmt) { \
260 const type *src0 = src; \
262 for (i = 0; i < size; i++) { \
263 float in = *src0 * c->gain + \
264 s->x[0] * c->cy[0] + \
265 s->x[1] * c->cy[1]; \
266 CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1]) \
274 void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
275 struct FFIIRFilterState *s, int size,
276 const int16_t *src, int sstep, int16_t *dst, int dstep)
279 FILTER_O2(int16_t, S16)
280 } else if (c->order == 4) {
281 FILTER_BW_O4(int16_t, S16)
283 FILTER_DIRECT_FORM_II(int16_t, S16)
287 void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
288 struct FFIIRFilterState *s, int size,
289 const float *src, int sstep, float *dst, int dstep)
292 FILTER_O2(float, FLT)
293 } else if (c->order == 4) {
294 FILTER_BW_O4(float, FLT)
296 FILTER_DIRECT_FORM_II(float, FLT)
300 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
305 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
314 void ff_iir_filter_init(FFIIRFilterContext *f) {
315 f->filter_flt = ff_iir_filter_flt;
318 ff_iir_filter_init_mips(f);
328 struct FFIIRFilterCoeffs *fcoeffs = NULL;
329 struct FFIIRFilterState *fstate = NULL;
330 float cutoff_coeff = 0.4;
331 int16_t x[SIZE], y[SIZE];
334 fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH,
335 FF_FILTER_MODE_LOWPASS, FILT_ORDER,
336 cutoff_coeff, 0.0, 0.0);
337 fstate = ff_iir_filter_init_state(FILT_ORDER);
339 for (i = 0; i < SIZE; i++) {
340 x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
343 ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
345 for (i = 0; i < SIZE; i++)
346 printf("%6d %6d\n", x[i], y[i]);
348 ff_iir_filter_free_coeffs(fcoeffs);
349 ff_iir_filter_free_state(fstate);