From ea12293e0a6764fb4655420de8e906bd42d90efd Mon Sep 17 00:00:00 2001
From: "Alfred E. Heggestad" <alfred.heggestad@gmail.com>
Date: Thu, 27 Apr 2017 20:30:31 +0200
Subject: aulevel: calculate audio levels in dBov

---
 src/aulevel.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/srcs.mk   |  1 +
 2 files changed, 86 insertions(+)
 create mode 100644 src/aulevel.c

(limited to 'src')

diff --git a/src/aulevel.c b/src/aulevel.c
new file mode 100644
index 0000000..bc9a27a
--- /dev/null
+++ b/src/aulevel.c
@@ -0,0 +1,85 @@
+/**
+ * @file src/aulevel.c  Audio level
+ *
+ * Copyright (C) 2017 Creytiv.com
+ */
+
+#include <math.h>
+#include <re.h>
+#include <baresip.h>
+#include "core.h"
+
+
+/**
+ * Generic routine to calculate RMS (Root-Mean-Square) from
+ * a set of signed 16-bit values
+ *
+ * \verbatim
+
+	     .---------------
+	     |   N-1
+	     |  ----.
+	     |  \
+	     |   \        2
+	     |    |   s[n]
+	     |   /
+	     |  /
+	 _   |  ----'
+	  \  |   n=0
+	   \ |  ------------
+	    \|       N
+
+   \endverbatim
+ *
+ * @param data Array of signed 16-bit values
+ * @param len  Number of values
+ *
+ * @return RMS value from 0 to 32768
+ */
+static double calc_rms(const int16_t *data, size_t len)
+{
+	double sum = 0;
+	size_t i;
+
+	if (!data || !len)
+		return .0;
+
+	for (i = 0; i < len; i++) {
+		const double sample = data[i];
+
+		sum += sample * sample;
+	}
+
+	return sqrt(sum / (double)len);
+}
+
+
+/**
+ * Calculate the audio level in dBov from a set of audio samples.
+ * dBov is the level, in decibels, relative to the overload point
+ * of the system
+ *
+ * @param sampv Audio samples
+ * @param sampc Number of audio samples
+ *
+ * @return Audio level expressed in dBov
+ */
+double aulevel_calc_dbov(const int16_t *sampv, size_t sampc)
+{
+	static const double peak = 32767.0;
+	double rms, dbov;
+
+	if (!sampv || !sampc)
+		return AULEVEL_MIN;
+
+	rms = calc_rms(sampv, sampc) / peak;
+
+	dbov = 20 * log10(rms);
+
+	if (dbov < AULEVEL_MIN)
+		dbov = AULEVEL_MIN;
+	else if (dbov > AULEVEL_MAX)
+		dbov = AULEVEL_MAX;
+
+	return dbov;
+}
diff --git a/src/srcs.mk b/src/srcs.mk
index c538600..cdb2a26 100644
--- a/src/srcs.mk
+++ b/src/srcs.mk
@@ -8,6 +8,7 @@ SRCS	+= account.c
 SRCS	+= aucodec.c
 SRCS	+= audio.c
 SRCS	+= aufilt.c
+SRCS	+= aulevel.c
 SRCS	+= auplay.c
 SRCS	+= ausrc.c
 SRCS	+= baresip.c
-- 
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