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A-Netz: Click removal when changing sequenced paging tones

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When tone changes to next tone, a transition of 2ms is performed. The last
tone is faded out and the new tone faded in.
This commit is contained in:
Andreas Eversberg
2016-11-13 17:45:46 +01:00
committed by Andreas Eversberg
parent 7a2ff388a4
commit 481181fa74
3 changed files with 39 additions and 7 deletions
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43
src/anetz/dsp.c
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@@ -37,7 +37,7 @@
* so both tones should be equal after pre-emphasis. This is why the paging
* tones is so much louder.*/
#define TX_PEAK_TONE 8192.0 /* peak amplitude for all tones */
#define TX_PEAK_PAGE 32767.0 /* peak amplitude paging tone */
#define TX_PEAK_PAGE 32766.0 /* peak amplitude paging tone */
// FIXME: what is the allowed deviation of tone?
#define CHUNK_DURATION 0.010 /* 10 ms */
@@ -68,6 +68,7 @@ void dsp_init(void)
for (i = 0; i < 256; i++) {
s = sin((double)i / 256.0 * 2.0 * PI);
dsp_sine_tone[i] = (int)(s * TX_PEAK_TONE);
s = cos((double)i / 256.0 * 2.0 * PI);
dsp_sine_page[i] = (int)(s * TX_PEAK_PAGE);
}
@@ -273,13 +274,20 @@ static void fsk_paging_tone(anetz_t *anetz, int16_t *samples, int length)
}
}
/* Generate audio stream of 4 sequenced paging tones. Keep phase for next call of function.
* Use TX_PEAK_PAGE / 2 for each tone, that is twice as much peak per tone. */
/* Generate audio stream of 4 sequenced paging tones. Keep phase for next call
* of function.
*
* Use TX_PEAK_PAGE / 2 for each tone, that is twice as much peak per tone.
*
* Click removal when changing tones that have individual phase:
* When tone changes to next tone, a transition of 2ms is performed. The last
* tone is faded out and the new tone faded in.
*/
static void fsk_paging_tone_sequence(anetz_t *anetz, int16_t *samples, int length, int numspl)
{
double phaseshift[4], phase[4];
int i;
int tone, count;
int tone, count, transition;
for (i = 0; i < 4; i++) {
phaseshift[i] = anetz->paging_phaseshift256[i];
@@ -287,9 +295,18 @@ static void fsk_paging_tone_sequence(anetz_t *anetz, int16_t *samples, int lengt
}
tone = anetz->paging_tone;
count = anetz->paging_count;
transition = anetz->paging_transition;
while (length) {
*samples++ = dsp_sine_page[((uint8_t)phase[tone]) & 0xff] >> 1;
/* use tone, but during transition of tones, keep phase 0 degrees (high level) until next tone reaches 0 degrees (high level) */
if (!transition)
*samples++ = dsp_sine_page[((uint8_t)phase[tone]) & 0xff] >> 1;
else {
/* fade between old an new tone */
*samples++
= (double)dsp_sine_page[((uint8_t)phase[(tone - 1) & 3]) & 0xff] * (double)(transition - count) / (double)transition / 2.0
+ (double)dsp_sine_page[((uint8_t)phase[tone]) & 0xff] * (double)count / (double)transition / 2.0;
}
phase[0] += phaseshift[0];
phase[1] += phaseshift[1];
phase[2] += phaseshift[2];
@@ -298,7 +315,16 @@ static void fsk_paging_tone_sequence(anetz_t *anetz, int16_t *samples, int lengt
if (phase[1] >= 256) phase[1] -= 256;
if (phase[2] >= 256) phase[2] -= 256;
if (phase[3] >= 256) phase[3] -= 256;
if (++count == numspl) {
count++;
if (transition && count == transition) {
transition = 0;
/* reset counter again, when transition ends */
count = 0;
}
if (count >= numspl) {
/* start transition to next tone (lasts 2 ms) */
transition = anetz->sender.samplerate / 500;
/* reset counter here, when transition starts */
count = 0;
if (++tone == 4)
tone = 0;
@@ -311,6 +337,7 @@ static void fsk_paging_tone_sequence(anetz_t *anetz, int16_t *samples, int lengt
}
anetz->paging_tone = tone;
anetz->paging_count = count;
anetz->paging_transition = transition;
}
/* Generate audio stream from tone. Keep phase for next call of function. */
@@ -360,5 +387,9 @@ void anetz_set_dsp_mode(anetz_t *anetz, enum dsp_mode mode)
{
PDEBUG(DDSP, DEBUG_DEBUG, "DSP mode %d -> %d\n", anetz->dsp_mode, mode);
anetz->dsp_mode = mode;
/* reset sequence paging */
anetz->paging_tone = 0;
anetz->paging_count = 0;
anetz->paging_transition = 0;
}