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Improvement of Goertzel filter. Using Hamming window now. Add test routine.

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This commit is contained in:
Andreas Eversberg
2021-11-28 13:11:19 +01:00
parent d1f6a0f6ce
commit dde4113e61
8 changed files with 108 additions and 24 deletions
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15
src/nmt/dsp.c
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@@ -64,7 +64,7 @@
#define MAX_DISPLAY 1.4 /* something above speech level */
#define DIALTONE_HZ 425.0 /* dial tone frequency */
#define TX_PEAK_DIALTONE 1.0 /* dial tone peak FIXME: Not found in the specs! */
#define SUPER_DURATION 0.25 /* duration of supervisory signal measurement */
#define SUPER_BANDWIDTH 30.0 /* distance between two SAT tones, also bandwidth for goertzel filter */
#define SUPER_PRINT 2 /* print supervisory signal measurement every 0.5 seconds */
#define SUPER_LOST_COUNT 4 /* number of measures to loose supervisory signal */
#define SUPER_DETECT_COUNT 6 /* number of measures to detect supervisory signal */
@@ -76,7 +76,7 @@ static double super_freq[5] = {
3985.0, /* 0-Signal 2 */
4015.0, /* 0-Signal 3 */
4045.0, /* 0-Signal 4 */
3900.0, /* noise level to check against */
3895.0, /* noise level to check against */
};
/* table for fast sine generation */
@@ -129,8 +129,11 @@ int dsp_init_sender(nmt_t *nmt, double deviation_factor)
return -EINVAL;
}
/* allocate ring buffer for supervisory signal detection */
nmt->super_samples = (int)((double)nmt->sender.samplerate * SUPER_DURATION + 0.5);
/* allocate ring buffer for SAT signal detection
* the bandwidth of the Goertzel filter is the reciprocal of the duration
* we half our bandwidth, so that other supervisory signals will be canceled out completely by goertzel filter
*/
nmt->super_samples = (int)((double)nmt->sender.samplerate * (1.0 / (SUPER_BANDWIDTH / 2)) + 0.5);
spl = calloc(1, nmt->super_samples * sizeof(*spl));
if (!spl) {
PDEBUG(DDSP, DEBUG_ERROR, "No memory!\n");
@@ -260,7 +263,7 @@ static void fsk_receive_bit(void *inst, int bit, double quality, double level)
nmt_receive_frame(nmt, nmt->rx_frame, quality, level, frames_elapsed);
}
/* compare supervisory signal against noise floor on 3900 Hz */
/* compare supervisory signal against noise floor around 3895 Hz */
static void super_decode(nmt_t *nmt, sample_t *samples, int length)
{
double result[2], level, quality;
@@ -269,7 +272,7 @@ static void super_decode(nmt_t *nmt, sample_t *samples, int length)
audio_goertzel(&nmt->super_goertzel[4], samples, length, 0, &result[1], 1); /* noise floor detection */
/* normalize supervisory level */
level = result[0] / 0.63662 / TX_PEAK_SUPER;
level = result[0] / TX_PEAK_SUPER;
quality = (result[0] - result[1]) / result[0];
if (quality < 0)