initial git import

src/common/loss.c

@@ -0,0 +1,93 @@
+/* Loss detection
+ *
+ * (C) 2016 by Andreas Eversberg <jolly@eversberg.eu>
+ * All Rights Reserved
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <math.h>
+#include "../common/debug.h"
+#include "loss.h"
+
+/* initialize detector
+ *
+ * interval: number of detector calls for one interval of one second
+ * threshold: intervals may differ by this factor, to be declared as similar
+ *            0 to disable, e.g. 1.3 for 30 percent change
+ */
+void audio_init_loss(loss_t *loss, int interval, double threshold, int seconds)
+{
+	memset(loss, 0, sizeof(*loss));
+
+	loss->interval = interval;
+	loss->threshold = threshold;
+	loss->interval_num = seconds;
+}
+
+/* call this when tones/telegrams are detected */
+void audio_reset_loss(loss_t *loss)
+{
+	if (loss->interval_count > 0) {
+		PDEBUG(DAUDIO, DEBUG_DEBUG, "Signal is recovered (loss is gone).\n");
+		loss->interval_count = 0;
+	}
+	loss->level = 0;
+	loss->level_count = 0;
+}
+
+#define LOSS_MAX_DIFF 	1.1	/* 10 % difference */
+
+/* call this for every interval */
+int audio_detect_loss(loss_t *loss, double level)
+{
+	double diff;
+			
+	/* disabled */
+	if (loss->threshold == 0.0)
+		return 0;
+
+	/* calculate a total level to detect loss */
+	loss->level += level;
+
+	if (++loss->level_count < loss->interval) 
+		return 0;
+
+	/* normalize level */
+	loss->level = loss->level / loss->level_count;
+
+	PDEBUG(DAUDIO, DEBUG_DEBUG, "Noise level = %.0f%%\n", loss->level * 100);
+
+	diff = loss->level / loss->level_last;
+	if (diff < 1.0)
+		diff = 1.0 / diff;
+	loss->level_last = loss->level;
+	loss->level = 0;
+	loss->level_count = 0;
+	if (diff < LOSS_MAX_DIFF && loss->level_last > loss->threshold) {
+		loss->interval_count++;
+		PDEBUG(DAUDIO, DEBUG_DEBUG, "Detected signal loss %d for intervals level change %.0f%% (below %.0f%%).\n", loss->interval_count, diff * 100 - 100, LOSS_MAX_DIFF * 100 - 100);
+	} else if (loss->interval_count > 0) {
+		audio_reset_loss(loss);
+	}
+
+	if (loss->interval_count == loss->interval_num)
+		return 1;
+	return 0;
+}
+