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#include <stdio.h>
#include <stdint.h>
#include <math.h>
#include <string.h>
#include "../common/emphasis.h"
#define level2db(level) (20 * log10(level))
#define db2level(db) pow(10, (double)db / 20.0)
#define SAMPLERATE 48000
#define DEVIATION 8000.0
static void check_level(int16_t *samples, const char *desc)
{
int i;
int last = 0, envelope = 0;
int up = 0;
int freq;
for (i = 0; i < SAMPLERATE; i++) {
if (last < samples[i]) {
up = 1;
} else if (last > samples[i]) {
if (up) {
envelope = last;
}
up = 0;
}
if ((i % (SAMPLERATE/40)) == 0) {
freq = 500 + 500 * (i / (SAMPLERATE / 8));
printf("%s: f = %d envelop = %.4f\n", desc, freq, level2db((double)envelope / DEVIATION));
}
last = samples[i];
}
}
static void gen_samples(int16_t *samples)
{
int i;
double value;
int freq;
for (i = 0; i < SAMPLERATE; i++) {
freq = 500 + 500 * (i / (SAMPLERATE / 8));
value = sin(2.0 * M_PI * (double)freq / (double)SAMPLERATE * (double)i);
samples[i] = value * DEVIATION;
}
}
int main(void)
{
emphasis_t estate;
int16_t samples[SAMPLERATE];
printf("1000 Hz shall be close to 0 dB, that is no significant change in volume.\n\n");
/* generate sweep 0..4khz */
gen_samples(samples);
init_emphasis(&estate, SAMPLERATE);
// check_level(samples, "unchanged");
pre_emphasis(&estate, samples, SAMPLERATE);
check_level(samples, "pre-emphasis");
/* generate sweep 0..4khz */
gen_samples(samples);
de_emphasis(&estate, samples, SAMPLERATE);
check_level(samples, "de-emphasis");
return 0;
}
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