3 * Copyright (c) 2017 Rostislav Pehlivanov <atomnuker@gmail.com>
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
22 #ifndef AVCODEC_OPUSENC_UTILS_H
23 #define AVCODEC_OPUSENC_UTILS_H
27 typedef struct FFBesselFilter {
34 /* Fills the coefficients, returns 1 if filter will be unstable */
35 static inline int bessel_reinit(FFBesselFilter *s, float n, float f0, float fs,
39 float c, cfreq, w0, k1, k2;
42 c = (1.0f/sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f))/sqrtf(3.0f);
44 unstable = (cfreq <= 0.0f || cfreq >= 1.0f/4.0f);
46 c = sqrtf(3.0f)*sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f);
47 cfreq = 0.5f - c*f0/fs;
48 unstable = (cfreq <= 3.0f/8.0f || cfreq >= 1.0f/2.0f);
51 w0 = tanf(M_PI*cfreq);
55 s->a[0] = k2/(1.0f + k1 + k2);
56 s->a[1] = 2.0f * s->a[0];
58 s->b[0] = 2.0f * s->a[0] * (1.0f/k2 - 1.0f);
59 s->b[1] = 1.0f - (s->a[0] + s->a[1] + s->a[2] + s->b[0]);
69 static inline int bessel_init(FFBesselFilter *s, float n, float f0, float fs,
72 memset(s, 0, sizeof(FFBesselFilter));
73 return bessel_reinit(s, n, f0, fs, highpass);
76 static inline float bessel_filter(FFBesselFilter *s, float x)
83 s->y[0] = s->a[0]*s->x[0] + s->a[1]*s->x[1] + s->a[2]*s->x[2] + s->b[0]*s->y[1] + s->b[1]*s->y[2];
87 #endif /* AVCODEC_OPUSENC_UTILS_H */