williamp/osmocom-analog
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

C-Netz: Use emphasis with 200 uS time constant

Browse Source
This commit is contained in:
Andreas Eversberg
2016-10-23 08:46:05 +02:00
parent 8864db8269
commit 1ea95de120
6 changed files with 17 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
src/common/emphasis.c
View File

@@ -26,10 +26,9 @@
#define PI M_PI
#define CUT_OFF_E 300.0 /* cut-off frequency for emphasis filters */
#define CUT_OFF_H 300.0 /* cut-off frequency for high-pass filters */
#define CUT_OFF_H 200.0 /* cut-off frequency for high-pass filters */
int init_emphasis(emphasis_t *state, int samplerate)
int init_emphasis(emphasis_t *state, int samplerate, double cut_off)
{
double factor, rc, dt;
@@ -40,13 +39,15 @@ int init_emphasis(emphasis_t *state, int samplerate)
}
/* exp (-2 * PI * CUT_OFF * delta_t) */
factor = exp(-2.0 * PI * CUT_OFF_E / samplerate); /* 1/samplerate == delta_t */
factor = exp(-2.0 * PI * cut_off / samplerate); /* 1/samplerate == delta_t */
PDEBUG(DDSP, DEBUG_DEBUG, "Emphasis factor = %.3f\n", factor);
state->p.factor = factor;
state->p.amp = samplerate / 6350.0;
state->p.amp = samplerate / 6400.0;
state->d.d_factor = factor;
state->d.amp = 1.0 / (samplerate / 5550.0);
state->d.amp = 1.0 / (samplerate / 5750.0);
/* high-pass filter prevents low frequency noise and dc level
* from being amplified by de-emphasis */
rc = 1.0 / (CUT_OFF_H * 2.0 *3.14);
dt = 1.0 / samplerate;
state->d.h_factor = rc / (rc + dt);

4
src/common/emphasis.h
View File

@@ -13,7 +13,9 @@ typedef struct emphasis {
} d;
} emphasis_t;
int init_emphasis(emphasis_t *state, int samplerate);
#define CUT_OFF_EMPHASIS_DEFAULT 300.0
int init_emphasis(emphasis_t *state, int samplerate, double cut_off);
void pre_emphasis(emphasis_t *state, int16_t *samples, int num);
void de_emphasis(emphasis_t *state, int16_t *samples, int num);

2
src/common/sender.c
View File

@@ -130,7 +130,7 @@ int sender_create(sender_t *sender, int kanal, const char *sounddev, int sampler
}
}
rc = init_emphasis(&sender->estate, samplerate);
rc = init_emphasis(&sender->estate, samplerate, CUT_OFF_EMPHASIS_DEFAULT);
if (rc < 0)
goto error;