Reduce range of volume effect (limit to -50 - +50 dB), and use logarithmic scale in timeline.

Related to #770

data/effects/volume.xml

@@ -3,7 +3,7 @@
 	<name>Volume (keyframable)</name>
 	<description>Adjust audio volume with keyframes</description>
 	<author>Dan Dennedy</author>
-	<parameter type="animated" name="level" default="0" max="60" min="-100" suffix="dB" scale="-1">
+	<parameter type="animated" name="level" default="0" max="50" min="-50" suffix="dB" scale="-1">
 		<name>Gain</name>
 	</parameter>
 </effect>

src/assets/keyframes/model/keyframemodel.cpp

@@ -305,9 +305,9 @@ bool KeyframeModel::updateKeyframe(int pos, double newVal)
         int logRole = ptr->data(m_index, AssetParameterModel::ScaleRole).toInt();
         double realValue;
         if (logRole == -1) {
-            // Logarythmic scale for lower than norm values
+            // Logarythmic scale
             if (newVal >= 0.5) {
-                realValue = norm + (2 * (newVal - 0.5) * (max / factor - norm));
+                realValue = norm + pow(2 * (newVal - 0.5), 10.0 / 6) * (max / factor - norm);
             } else {
                 realValue = norm - pow(2 * (0.5 - newVal), 10.0 / 6) * (norm - min / factor);
             }
@@ -461,11 +461,12 @@ QVariant KeyframeModel::data(const QModelIndex &index, int role) const
             int logRole = ptr->data(m_index, AssetParameterModel::ScaleRole).toInt();
             double linear = val * factor;
             if (logRole == -1) {
-                // Logarythmic scale for lower than norm values
+                // Logarythmic scale
+                // transform current value to 0..1 scale
                 if (linear >= norm) {
-                    return 0.5 + (linear - norm) / (max * factor - norm) * 0.5;
+                    double scaled = (linear - norm) / (max * factor - norm);
+                    return 0.5 + pow(scaled, 0.6) * 0.5;
                 }
-                // transform current value to 0..1 scale
                 double scaled = (linear - norm) / (min * factor - norm);
                 // Log scale
                 return 0.5 - pow(scaled, 0.6) * 0.5;
@@ -896,9 +897,9 @@ QVariant KeyframeModel::getNormalizedValue(double newVal) const
         int logRole = ptr->data(m_index, AssetParameterModel::ScaleRole).toInt();
         double realValue;
         if (logRole == -1) {
-            // Logarythmic scale for lower than norm values
+            // Logarythmic scale
             if (newVal >= 0.5) {
-                realValue = norm + (2 * (newVal - 0.5) * (max / factor - norm));
+                realValue = norm + pow(2 * (newVal - 0.5), 10.0 / 6) * (max / factor - norm);
             } else {
                 realValue = norm - pow(2 * (0.5 - newVal), 10.0 / 6) * (norm - min / factor);
             }