OpenSL: Fix volume scale

The old code was assuming that the interface was expecting power
values, while it actually uses amplitude values. In addition the
difference between the min/max values where used, resulting in
quite high gain values.

Task-number: QTBUG-34777

Change-Id: Ibd3f7774b67c44e37dfd79cbe6e2c35746f00a0a
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>

diff --git a/src/plugins/opensles/qopenslesaudiooutput.cpp b/src/plugins/opensles/qopenslesaudiooutput.cpp
index 65c0f5a..df91e6f 100644 (file)
--- a/src/plugins/opensles/qopenslesaudiooutput.cpp
+++ b/src/plugins/opensles/qopenslesaudiooutput.cpp
@@ -52,6 +52,8 @@
 #define BUFFER_COUNT 2
 #define DEFAULT_PERIOD_TIME_MS 50
 #define MINIMUM_PERIOD_TIME_MS 5
+#define EBASE 2.302585093
+#define LOG10(x) qLn(x)/qreal(EBASE)
 
 QT_BEGIN_NAMESPACE
 
@@ -622,7 +624,7 @@ inline SLmillibel QOpenSLESAudioOutput::adjustVolume(qreal vol)
     if (qFuzzyCompare(vol, qreal(1.0)))
         return 0;
 
-    return SL_MILLIBEL_MIN + ((1 - (qLn(10 - (vol * 10)) / qLn(10))) * SL_MILLIBEL_MAX);
+    return 20 * LOG10(vol) * 100; // I.e., 20 * LOG10(SL_MILLIBEL_MAX * vol / SL_MILLIBEL_MAX)
 }
 
 QT_END_NAMESPACE