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"
31 * IIR filter global parameters
33 typedef struct FFIIRFilterCoeffs{
43 typedef struct FFIIRFilterState{
47 /// maximum supported filter order
50 static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
51 enum IIRFilterMode filt_mode,
52 int order, float cutoff_ratio,
57 double p[MAXORDER + 1][2];
59 if (filt_mode != FF_FILTER_MODE_LOWPASS) {
60 av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
61 "low-pass filter mode\n");
65 av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
66 "even filter orders\n");
70 wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
73 for(i = 1; i < (order >> 1) + 1; i++)
74 c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
78 for(i = 1; i <= order; i++)
79 p[i][0] = p[i][1] = 0.0;
80 for(i = 0; i < order; i++){
82 double th = (i + (order >> 1) + 0.5) * M_PI / order;
83 double a_re, a_im, c_re, c_im;
90 zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
91 zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
93 for(j = order; j >= 1; j--)
97 p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
98 p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
100 a_re = p[0][0]*zp[0] - p[0][1]*zp[1];
101 p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
104 c->gain = p[order][0];
105 for(i = 0; i < order; i++){
107 c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
108 (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
110 c->gain /= 1 << order;
115 static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
116 enum IIRFilterMode filt_mode, int order,
117 float cutoff_ratio, float stopband)
119 double cos_w0, sin_w0;
122 if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
123 filt_mode != FF_FILTER_MODE_LOWPASS) {
124 av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
125 "high-pass and low-pass filter modes\n");
129 av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
133 cos_w0 = cos(M_PI * cutoff_ratio);
134 sin_w0 = sin(M_PI * cutoff_ratio);
136 a0 = 1.0 + (sin_w0 / 2.0);
138 if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
139 c->gain = ((1.0 + cos_w0) / 2.0) / a0;
140 x0 = ((1.0 + cos_w0) / 2.0) / a0;
141 x1 = (-(1.0 + cos_w0)) / a0;
142 } else { // FF_FILTER_MODE_LOWPASS
143 c->gain = ((1.0 - cos_w0) / 2.0) / a0;
144 x0 = ((1.0 - cos_w0) / 2.0) / a0;
145 x1 = (1.0 - cos_w0) / a0;
147 c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0;
148 c->cy[1] = (2.0 * cos_w0) / a0;
150 // divide by gain to make the x coeffs integers.
151 // during filtering, the delay state will include the gain multiplication
152 c->cx[0] = lrintf(x0 / c->gain);
153 c->cx[1] = lrintf(x1 / c->gain);
158 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
159 enum IIRFilterType filt_type,
160 enum IIRFilterMode filt_mode,
161 int order, float cutoff_ratio,
162 float stopband, float ripple)
164 FFIIRFilterCoeffs *c;
167 if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
170 FF_ALLOCZ_OR_GOTO(avc, c, sizeof(FFIIRFilterCoeffs),
172 FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
174 FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
179 case FF_FILTER_TYPE_BUTTERWORTH:
180 ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
183 case FF_FILTER_TYPE_BIQUAD:
184 ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
188 av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
196 ff_iir_filter_free_coeffs(c);
200 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
202 FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
206 #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
208 #define CONV_FLT(dest, source) dest = source;
210 #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt) \
211 in = *src0 * c->gain \
212 + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \
213 + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
214 res = (s->x[i0] + in )*1 \
215 + (s->x[i1] + s->x[i3])*4 \
217 CONV_##fmt(*dst0, res) \
222 #define FILTER_BW_O4(type, fmt) { \
224 const type *src0 = src; \
226 for (i = 0; i < size; i += 4) { \
228 FILTER_BW_O4_1(0, 1, 2, 3, fmt); \
229 FILTER_BW_O4_1(1, 2, 3, 0, fmt); \
230 FILTER_BW_O4_1(2, 3, 0, 1, fmt); \
231 FILTER_BW_O4_1(3, 0, 1, 2, fmt); \
235 #define FILTER_DIRECT_FORM_II(type, fmt) { \
237 const type *src0 = src; \
239 for (i = 0; i < size; i++) { \
242 in = *src0 * c->gain; \
243 for(j = 0; j < c->order; j++) \
244 in += c->cy[j] * s->x[j]; \
245 res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; \
246 for(j = 1; j < c->order >> 1; j++) \
247 res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; \
248 for(j = 0; j < c->order - 1; j++) \
249 s->x[j] = s->x[j + 1]; \
250 CONV_##fmt(*dst0, res) \
251 s->x[c->order - 1] = in; \
257 #define FILTER_O2(type, fmt) { \
259 const type *src0 = src; \
261 for (i = 0; i < size; i++) { \
262 float in = *src0 * c->gain + \
263 s->x[0] * c->cy[0] + \
264 s->x[1] * c->cy[1]; \
265 CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1]) \
273 void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
274 struct FFIIRFilterState *s, int size,
275 const int16_t *src, int sstep, int16_t *dst, int dstep)
278 FILTER_O2(int16_t, S16)
279 } else if (c->order == 4) {
280 FILTER_BW_O4(int16_t, S16)
282 FILTER_DIRECT_FORM_II(int16_t, S16)
286 void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
287 struct FFIIRFilterState *s, int size,
288 const float *src, int sstep, float *dst, int dstep)
291 FILTER_O2(float, FLT)
292 } else if (c->order == 4) {
293 FILTER_BW_O4(float, FLT)
295 FILTER_DIRECT_FORM_II(float, FLT)
299 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
304 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
321 struct FFIIRFilterCoeffs *fcoeffs = NULL;
322 struct FFIIRFilterState *fstate = NULL;
323 float cutoff_coeff = 0.4;
324 int16_t x[SIZE], y[SIZE];
327 fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH,
328 FF_FILTER_MODE_LOWPASS, FILT_ORDER,
329 cutoff_coeff, 0.0, 0.0);
330 fstate = ff_iir_filter_init_state(FILT_ORDER);
332 for (i = 0; i < SIZE; i++) {
333 x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
336 ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
338 for (i = 0; i < SIZE; i++)
339 printf("%6d %6d\n", x[i], y[i]);
341 ff_iir_filter_free_coeffs(fcoeffs);
342 ff_iir_filter_free_state(fstate);