C-Netz: Use emphasis with 200 uS time constant
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8864db8269
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1ea95de120
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@ -422,7 +422,7 @@ int amps_create(int channel, enum amps_chan_type chan_type, const char *sounddev
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amps->pre_emphasis = pre_emphasis;
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amps->de_emphasis = de_emphasis;
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rc = init_emphasis(&s->estate, samplerate);
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rc = init_emphasis(&s->estate, samplerate, CUT_OFF_EMPHASIS_DEFAULT);
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if (rc < 0)
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goto error;
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@ -105,6 +105,8 @@
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/* uncomment this to do echo debugging (-L) on Speech Channel */
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//#define DEBUG_SPK
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#define CUT_OFF_EMPHASIS_CNETZ 796 /* 200 uS time constant */
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/* Call reference for calls from mobile station to network
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This offset of 0x400000000 is required for MNCC interface. */
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static int new_callref = 0x40000000;
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@ -286,7 +288,7 @@ int cnetz_create(int kanal, enum cnetz_chan_type chan_type, const char *sounddev
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cnetz->pre_emphasis = pre_emphasis;
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cnetz->de_emphasis = de_emphasis;
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rc = init_emphasis(&cnetz->estate, samplerate);
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rc = init_emphasis(&cnetz->estate, samplerate, CUT_OFF_EMPHASIS_CNETZ);
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if (rc < 0)
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goto error;
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@ -26,10 +26,9 @@
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#define PI M_PI
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#define CUT_OFF_E 300.0 /* cut-off frequency for emphasis filters */
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#define CUT_OFF_H 300.0 /* cut-off frequency for high-pass filters */
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#define CUT_OFF_H 200.0 /* cut-off frequency for high-pass filters */
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int init_emphasis(emphasis_t *state, int samplerate)
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int init_emphasis(emphasis_t *state, int samplerate, double cut_off)
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{
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double factor, rc, dt;
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@ -40,13 +39,15 @@ int init_emphasis(emphasis_t *state, int samplerate)
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}
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/* exp (-2 * PI * CUT_OFF * delta_t) */
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factor = exp(-2.0 * PI * CUT_OFF_E / samplerate); /* 1/samplerate == delta_t */
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factor = exp(-2.0 * PI * cut_off / samplerate); /* 1/samplerate == delta_t */
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PDEBUG(DDSP, DEBUG_DEBUG, "Emphasis factor = %.3f\n", factor);
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state->p.factor = factor;
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state->p.amp = samplerate / 6350.0;
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state->p.amp = samplerate / 6400.0;
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state->d.d_factor = factor;
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state->d.amp = 1.0 / (samplerate / 5550.0);
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state->d.amp = 1.0 / (samplerate / 5750.0);
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/* high-pass filter prevents low frequency noise and dc level
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* from being amplified by de-emphasis */
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rc = 1.0 / (CUT_OFF_H * 2.0 *3.14);
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dt = 1.0 / samplerate;
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state->d.h_factor = rc / (rc + dt);
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@ -13,7 +13,9 @@ typedef struct emphasis {
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} d;
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} emphasis_t;
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int init_emphasis(emphasis_t *state, int samplerate);
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#define CUT_OFF_EMPHASIS_DEFAULT 300.0
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int init_emphasis(emphasis_t *state, int samplerate, double cut_off);
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void pre_emphasis(emphasis_t *state, int16_t *samples, int num);
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void de_emphasis(emphasis_t *state, int16_t *samples, int num);
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@ -130,7 +130,7 @@ int sender_create(sender_t *sender, int kanal, const char *sounddev, int sampler
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}
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}
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rc = init_emphasis(&sender->estate, samplerate);
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rc = init_emphasis(&sender->estate, samplerate, CUT_OFF_EMPHASIS_DEFAULT);
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if (rc < 0)
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goto error;
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@ -11,7 +11,7 @@
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#define SAMPLERATE 48000
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#define DEVIATION 8000.0
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static double test_freq[] = { 25, 50, 100, 150, 200, 250, 300, 350, 400, 500, 1000, 2000, 4000, 0 };
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static double test_freq[] = { 25, 50, 100, 200, 250, 300, 400, 500, 1000, 2000, 4000, 0 };
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static void check_level(int16_t *samples, double freq, const char *desc)
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{
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@ -55,7 +55,7 @@ int main(void)
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printf("1000 Hz shall be close to 0 dB, that is no significant change in volume.\n\n");
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init_emphasis(&estate, SAMPLERATE);
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init_emphasis(&estate, SAMPLERATE, CUT_OFF_EMPHASIS_DEFAULT);
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for (i = 0; test_freq[i]; i++) {
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gen_samples(samples, test_freq[i]);
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