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Filter improvement: LP and HP filters, added test function

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The -3 dB level at cut-off frequency is now maintained for multiple
iterations.
This commit is contained in:
Andreas Eversberg
2017-01-15 11:08:42 +01:00
parent 799b96c801
commit ac0da3f76e
10 changed files with 186 additions and 32 deletions
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10
src/test/Makefile.am
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@@ -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 = \

125
src/test/test_filter.c Normal file
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@@ -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;
}