From ac0da3f76ee3f31599b0c572ed296b251e94378b Mon Sep 17 00:00:00 2001
From: Andreas Eversberg <jolly@eversberg.eu>
Date: Sun, 15 Jan 2017 11:08:42 +0100
Subject: Filter improvement: LP and HP filters, added test function

The -3 dB level at cut-off frequency is now maintained for multiple
iterations.
---
 src/test/Makefile.am   |  10 ++++
 src/test/test_filter.c | 125 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 135 insertions(+)
 create mode 100644 src/test/test_filter.c

(limited to 'src/test')

diff --git a/src/test/Makefile.am b/src/test/Makefile.am
index 25211d2..eace0dc 100644
--- a/src/test/Makefile.am
+++ b/src/test/Makefile.am
@@ -2,11 +2,21 @@ AUTOMAKE_OPTIONS = subdir-objects
 AM_CPPFLAGS = -Wall -g $(all_includes)
 
 noinst_PROGRAMS = \
+	test_filter \
 	test_compandor \
 	test_emphasis \
 	test_dms \
 	test_sms
 
+test_filter_SOURCES = test_filter.c dummy.c
+
+test_filter_LDADD = \
+	$(COMMON_LA) \
+	$(top_builddir)/src/common/libcommon.a \
+	$(ALSA_LIBS) \
+	$(UHD_LIBS) \
+	-lm
+
 test_compandor_SOURCES = test_compandor.c
 
 test_compandor_LDADD = \
diff --git a/src/test/test_filter.c b/src/test/test_filter.c
new file mode 100644
index 0000000..8c82292
--- /dev/null
+++ b/src/test/test_filter.c
@@ -0,0 +1,125 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <math.h>
+#include <string.h>
+#include "../common/filter.h"
+#include "../common/debug.h"
+
+#define level2db(level)		(20 * log10(level))
+#define db2level(db)		pow(10, (double)db / 20.0)
+
+#define SAMPLERATE	48000
+
+static double get_level(double *samples)
+{
+#if 0
+	int i;
+	double last = 0, envelope = 0;
+	int up = 0;
+
+	for (i = SAMPLERATE/2; i < SAMPLERATE; i++) {
+		if (last < samples[i]) {
+			up = 1;
+		} else if (last > samples[i]) {
+			if (up) {
+				if (last > envelope)
+					envelope = last;
+			}
+			up = 0;
+		}
+		last = samples[i];
+	}
+#else
+	int i;
+	double envelope = 0;
+	for (i = SAMPLERATE/2; i < SAMPLERATE; i++) {
+		if (samples[i] > envelope)
+			envelope = samples[i];
+	}
+#endif
+
+	return envelope;
+}
+
+static void gen_samples(double *samples, double freq)
+{
+	int i;
+	double value;
+
+	for (i = 0; i < SAMPLERATE; i++) {
+		value = cos(2.0 * M_PI * freq / (double)SAMPLERATE * (double)i);
+		samples[i] = value;
+	}
+}
+
+int main(void)
+{
+	filter_t filter_low;
+	filter_t filter_high;
+	double samples[SAMPLERATE];
+	double level;
+	int iter = 2;
+	int i;
+
+	debuglevel = DEBUG_DEBUG;
+
+	printf("testing low-pass filter with %d iterations\n", iter);
+
+	filter_lowpass_init(&filter_low, 1000.0, SAMPLERATE, iter);
+
+	for (i = 0; i < 4001; i += 100) {
+		gen_samples(samples, (double)i);
+		filter_process(&filter_low, samples, SAMPLERATE);
+		level = get_level(samples);
+		printf("%4d Hz: %.1f dB", i, level2db(level));
+		if (i == 1000)
+			printf(" cutoff\n");
+		else if (i == 2000)
+			printf(" double frequency\n");
+		else if (i == 4000)
+			printf(" quad frequency\n");
+		else
+			printf("\n");
+	}
+
+	printf("testing high-pass filter with %d iterations\n", iter);
+
+	filter_highpass_init(&filter_high, 2000.0, SAMPLERATE, iter);
+
+	for (i = 0; i < 4001; i += 100) {
+		gen_samples(samples, (double)i);
+		filter_process(&filter_high, samples, SAMPLERATE);
+		level = get_level(samples);
+		printf("%4d Hz: %.1f dB", i, level2db(level));
+		if (i == 2000)
+			printf(" cutoff\n");
+		else if (i == 1000)
+			printf(" half frequency\n");
+		else if (i == 500)
+			printf(" quarter frequency\n");
+		else
+			printf("\n");
+	}
+
+	printf("testing band-pass filter with %d iterations\n", iter);
+
+	filter_lowpass_init(&filter_low, 2000.0, SAMPLERATE, iter);
+	filter_highpass_init(&filter_high, 1000.0, SAMPLERATE, iter);
+
+	for (i = 0; i < 4001; i += 100) {
+		gen_samples(samples, (double)i);
+		filter_process(&filter_low, samples, SAMPLERATE);
+		filter_process(&filter_high, samples, SAMPLERATE);
+		level = get_level(samples);
+		printf("%4d Hz: %.1f dB", i, level2db(level));
+		if (i == 1000)
+			printf(" cutoff high\n");
+		else if (i == 2000)
+			printf(" cutoff low\n");
+		else
+			printf("\n");
+	}
+
+	return 0;
+}
+
-- 
cgit v1.2.3