aboutsummaryrefslogtreecommitdiffstats
path: root/src/libfilter/iir_filter.c
blob: 2f6bb1d96e7ab712c57388802b4307325714fbc4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
/* cut-off filter (biquad) based on Nigel Redmon (www.earlevel.com)
 *
 * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
 * All Rights Reserved
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include "../common/sample.h"
#include "iir_filter.h"

#define PI M_PI

void iir_lowpass_init(iir_filter_t *filter, double frequency, int samplerate, int iterations)
{
	double Fc, Q, K, norm;

	if (iterations > 64) {
		fprintf(stderr, "%s failed: too many iterations, please fix!\n", __func__);
		abort();
	}

	memset(filter, 0, sizeof(*filter));
	filter->iter = iterations;
	Q = pow(sqrt(0.5), 1.0 / (double)iterations); /* 0.7071 @ 1 iteration */
	Fc = frequency / (double)samplerate;
	K = tan(PI * Fc);
	norm = 1 / (1 + K / Q + K * K);
	filter->a0 = K * K * norm;
	filter->a1 = 2 * filter->a0;
	filter->a2 = filter->a0;
	filter->b1 = 2 * (K * K - 1) * norm;
	filter->b2 = (1 - K / Q + K * K) * norm;
}

void iir_highpass_init(iir_filter_t *filter, double frequency, int samplerate, int iterations)
{
	double Fc, Q, K, norm;

	memset(filter, 0, sizeof(*filter));
	filter->iter = iterations;
	Q = pow(sqrt(0.5), 1.0 / (double)iterations); /* 0.7071 @ 1 iteration */
	Fc = frequency / (double)samplerate;
	K = tan(PI * Fc);
	norm = 1 / (1 + K / Q + K * K);
	filter->a0 = 1 * norm;
	filter->a1 = -2 * filter->a0;
	filter->a2 = filter->a0;
	filter->b1 = 2 * (K * K - 1) * norm;
	filter->b2 = (1 - K / Q + K * K) * norm;
}

void iir_bandpass_init(iir_filter_t *filter, double frequency, int samplerate, int iterations)
{
	double Fc, Q, K, norm;

	memset(filter, 0, sizeof(*filter));
	filter->iter = iterations;
	Q = pow(sqrt(0.5), 1.0 / (double)iterations); /* 0.7071 @ 1 iteration */
	Fc = frequency / (double)samplerate;
	K = tan(PI * Fc);
	norm = 1 / (1 + K / Q + K * K);
	filter->a0 = K / Q * norm;
	filter->a1 = 0;
	filter->a2 = -filter->a0;
	filter->b1 = 2 * (K * K - 1) * norm;
	filter->b2 = (1 - K / Q + K * K) * norm;
}

void iir_notch_init(iir_filter_t *filter, double frequency, int samplerate, int iterations)
{
	double Fc, Q, K, norm;

	memset(filter, 0, sizeof(*filter));
	filter->iter = iterations;
	Q = pow(sqrt(0.5), 1.0 / (double)iterations); /* 0.7071 @ 1 iteration */
	Fc = frequency / (double)samplerate;
	K = tan(PI * Fc);
	norm = 1 / (1 + K / Q + K * K);
	filter->a0 = (1 + K * K) * norm;
	filter->a1 = 2 * (K * K - 1) * norm;
	filter->a2 = filter->a0;
	filter->b1 = filter->a1;
	filter->b2 = (1 - K / Q + K * K) * norm;
}
            
void iir_process(iir_filter_t *filter, sample_t *samples, int length)
{
	double a0, a1, a2, b1, b2;
	double *z1, *z2;
	double in, out;
	int iterations = filter->iter;
	int i, j;

	/* get states */
	a0 = filter->a0;
	a1 = filter->a1;
	a2 = filter->a2;
	b1 = filter->b1;
	b2 = filter->b2;

	/* these are state pointers, so no need to write back */
	z1 = filter->z1;
	z2 = filter->z2;

	/* process filter */
	for (i = 0; i < length; i++) {
		in = *samples;
		for (j = 0; j < iterations; j++) {
			out = in * a0 + z1[j];
			z1[j] = in * a1 + z2[j] - b1 * out;
			z2[j] = in * a2 - b2 * out;
			in = out;
		}
		*samples++ = in;
	}
}

void iir_process_baseband(iir_filter_t *filter, float *baseband, int length)
{
	double a0, a1, a2, b1, b2;
	double *z1, *z2;
	double in, out;
	int iterations = filter->iter;
	int i, j;

	/* get states */
	a0 = filter->a0;
	a1 = filter->a1;
	a2 = filter->a2;
	b1 = filter->b1;
	b2 = filter->b2;

	/* these are state pointers, so no need to write back */
	z1 = filter->z1;
	z2 = filter->z2;

	/* process filter */
	for (i = 0; i < length; i++) {
		in = *baseband;
		for (j = 0; j < iterations; j++) {
			out = in * a0 + z1[j];
			z1[j] = in * a1 + z2[j] - b1 * out;
			z2[j] = in * a2 - b2 * out;
			in = out;
		}
		*baseband = in;
		baseband += 2;
	}
}