aboutsummaryrefslogtreecommitdiffstats
path: root/src/libfilter/iir_filter.c
diff options
context:
space:
mode:
Diffstat (limited to 'src/libfilter/iir_filter.c')
-rw-r--r--src/libfilter/iir_filter.c167
1 files changed, 167 insertions, 0 deletions
diff --git a/src/libfilter/iir_filter.c b/src/libfilter/iir_filter.c
new file mode 100644
index 0000000..2f6bb1d
--- /dev/null
+++ b/src/libfilter/iir_filter.c
@@ -0,0 +1,167 @@
+/* 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;
+ }
+}
+