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-rw-r--r--ss5_encode.c102
1 files changed, 102 insertions, 0 deletions
diff --git a/ss5_encode.c b/ss5_encode.c
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+++ b/ss5_encode.c
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+/*
+ * SS5 signal coder.
+ *
+ * Copyright by Andreas Eversberg (jolly@eversberg.eu)
+ *
+ * This software may be used and distributed according to the terms
+ * of the GNU General Public License, incorporated herein by reference.
+ *
+ */
+
+#include "main.h"
+#include "ss5_encode.h"
+
+ /* 2*PI*f/8000 */
+static double ss5_freq[9][2] = {
+ {0.0, 0}, /* 0: 0 */
+ {700, 0.19952623}, /* 1: 700, -7db */
+ {900, 0.19952623}, /* 2: 900, -7db */
+ {1100, 0.19952623}, /* 3: 1100, -7db */
+ {1300, 0.19952623}, /* 4: 1300, -7db */
+ {1500, 0.19952623}, /* 5: 1500, -7db */
+ {1700, 0.19952623}, /* 6: 1700, -7db */
+ {2400, 0.12589254}, /* 7: 2400, -9db */
+ {2600, 0.12589254}, /* 8: 2600, -9db */
+};
+
+static char ss5_digits[][3] = {
+ {'1', 1, 2},
+ {'2', 1, 3},
+ {'3', 2, 3},
+ {'4', 1, 4},
+ {'5', 2, 4},
+ {'6', 3, 4},
+ {'7', 1, 5},
+ {'8', 2, 5},
+ {'9', 3, 5},
+ {'0', 4, 5},
+ {'*', 1, 6}, /* code 11 */
+ {'#', 2, 6}, /* code 12 */
+ {'a', 3, 6}, /* KP1 */
+ {'b', 4, 6}, /* KP2 */
+ {'c', 5, 6}, /* ST */
+ {'A', 7, 0}, /* 2400 answer, acknowledge */
+ {'B', 8, 0}, /* 2600 busy */
+ {'C', 7, 8}, /* 2600+2400 clear forward */
+ {0 , 0, 0},
+};
+
+static unsigned char sintab[15+3][8192]; /* sine tables of about one second sound (error <1Hz) */
+
+/* generate sine tables */
+void ss5_sine_generate(void)
+{
+ int i, j;
+ int cycles1, cycles2;
+ double vol1, vol2, phase1, phase2;
+ signed short sample;
+
+ for (i = 0; i < 15+3; i++) {
+ /* how many cycles are within 8192 samples (rounded!) */
+ cycles1 = (int)(ss5_freq[(int)ss5_digits[i][1]][0] / 8000.0 * 8192.0 + 0.5);
+ cycles2 = (int)(ss5_freq[(int)ss5_digits[i][2]][0] / 8000.0 * 8192.0 + 0.5);
+ /* how much phase shift within one cycle */
+ phase1 = 2.0 * 3.14159265 * cycles1 / 8192.0;
+ phase2 = 2.0 * 3.14159265 * cycles2 / 8192.0;
+ /* volume */
+ vol1 = ss5_freq[(int)ss5_digits[i][1]][1] * 32768.0;
+ vol2 = ss5_freq[(int)ss5_digits[i][2]][1] * 32768.0;
+ for (j = 0; j < 8192; j++) {
+ sample = (int)(sin(phase1 * j) * vol1);
+ sample += (int)(sin(phase2 * j) * vol2);
+ sintab[i][j] = audio_s16_to_law[sample & 0xffff];
+ }
+ }
+}
+
+/* encode digit at given sample_nr with given lengt and return law-encoded audio */
+unsigned char *ss5_encode(unsigned char *buffer, int len, char digit, int sample_nr)
+{
+ int i, j;
+
+ /* get frequency from digit */
+ i = 0;
+ while(ss5_digits[i][0]) {
+ if (digit == ss5_digits[i][0])
+ break;
+ i++;
+ }
+ if (!ss5_digits[i][0]) {
+ PERROR("Digit '%c' does not exist.\n", digit);
+ memset(buffer, audio_s16_to_law[0], sizeof(buffer));
+ return buffer;
+ }
+
+ /* copy tones */
+ for (j = 0; j < len; j++)
+ *buffer++ = sintab[i][sample_nr++ & 8191];
+
+ return buffer;
+}
+
+