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Work on emphasis filter: Neutral @ 1000 Hz; Use filter before de-emphasis

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This commit is contained in:
Andreas Eversberg
2017-01-28 08:02:11 +01:00
parent b3fd53b165
commit 71e556e7ff
5 changed files with 88 additions and 68 deletions
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64
src/test/test_emphasis.c
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@@ -3,6 +3,7 @@
#include <math.h>
#include <string.h>
#include "../common/sample.h"
#include "../common/filter.h"
#include "../common/emphasis.h"
#include "../common/debug.h"
@@ -10,29 +11,17 @@
#define db2level(db) pow(10, (double)db / 20.0)
#define SAMPLERATE 48000
#define DEVIATION 8000.0
static double test_freq[] = { 25, 50, 100, 200, 250, 300, 400, 500, 1000, 2000, 4000, 0 };
static void check_level(sample_t *samples, double freq, const char *desc)
static double get_level(double *samples)
{
int i;
int last = 0, envelope = 0;
int up = 0;
for (i = 0; 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];
double envelope = 0;
for (i = SAMPLERATE/2; i < SAMPLERATE; i++) {
if (samples[i] > envelope)
envelope = samples[i];
}
printf("%s: f = %.0f envelop = %.4f\n", desc, freq, level2db((double)envelope / DEVIATION));
return envelope;
}
static void gen_samples(double *samples, double freq)
@@ -41,34 +30,47 @@ static void gen_samples(double *samples, double freq)
double value;
for (i = 0; i < SAMPLERATE; i++) {
value = sin(2.0 * M_PI * freq / (double)SAMPLERATE * (double)i);
samples[i] = value * DEVIATION;
value = cos(2.0 * M_PI * freq / (double)SAMPLERATE * (double)i);
samples[i] = value;
}
}
int main(void)
{
emphasis_t estate;
double cut_off = CUT_OFF_EMPHASIS_DEFAULT;
double samples[SAMPLERATE];
int i;
double level;
double i;
debuglevel = DEBUG_DEBUG;
printf("1000 Hz shall be close to 0 dB, that is no significant change in volume.\n\n");
init_emphasis(&estate, SAMPLERATE, cut_off);
init_emphasis(&estate, SAMPLERATE, CUT_OFF_EMPHASIS_DEFAULT);
printf("testing pre-emphasis filter with cut-off frequency %.1f\n", cut_off);
for (i = 0; test_freq[i]; i++) {
gen_samples(samples, test_freq[i]);
for (i = 31.25; i < 4001; i = i * sqrt(sqrt(2.0))) {
gen_samples(samples, (double)i);
pre_emphasis(&estate, samples, SAMPLERATE);
check_level(samples, test_freq[i], "pre-emphasis");
level = get_level(samples);
printf("%s%.0f Hz: %.1f dB", debug_db(level), i, level2db(level));
if ((int)round(i) == 1000)
printf(" level=%.6f\n", level);
else
printf("\n");
}
/* generate sweep 0..4khz */
for (i = 0; test_freq[i]; i++) {
gen_samples(samples, test_freq[i]);
printf("testing de-emphasis filter with cut-off frequency %.1f\n", cut_off);
for (i = 31.25; i < 4001; i = i * sqrt(sqrt(2.0))) {
gen_samples(samples, (double)i);
de_emphasis(&estate, samples, SAMPLERATE);
check_level(samples, test_freq[i], "de-emphasis");
level = get_level(samples);
printf("%s%.0f Hz: %.1f dB", debug_db(level), i, level2db(level));
if ((int)round(i) == 1000)
printf(" level=%.6f\n", level);
else
printf("\n");
}
return 0;