diff --git a/libs/evoral/ControlList.cc b/libs/evoral/ControlList.cc
index 8ecdc5c423..b6e8111f4d 100644
--- a/libs/evoral/ControlList.cc
+++ b/libs/evoral/ControlList.cc
@@ -381,6 +381,14 @@ ControlList::thin (double thinning_factor)
 		return;
 	}
 
+	/* compat. In the past the actual (internal) value was used
+	 * to compute the area. For gain the range is 0..2 (exp).
+	 * Since we cannot change automation-thinning-factor
+	 * in user's existing config, we simply re-normalize
+	 * the thinning factor.
+	 */
+	thinning_factor *= .7071;
+
 	assert (is_sorted ());
 
 	bool changed = false;
@@ -407,9 +415,13 @@ ControlList::thin (double thinning_factor)
 				const double pw  = prev->when.samples ();
 				const double cw  = cur->when.samples ();
 
-				double area = fabs ((ppw * (prev->value - cur->value)) +
-				                    (pw * (cur->value - prevprev->value)) +
-				                    (cw * (prevprev->value - prev->value)));
+				const float ppv = _desc.to_interface (prevprev->value);
+				const float cv  = _desc.to_interface (cur->value);
+				const float pv  = _desc.to_interface (prev->value);
+
+				double area = fabs ((ppw * (pv - cv)) +
+				                    (pw * (cv - ppv)) +
+				                    (cw * (ppv - pv)));
 
 				if (area < thinning_factor) {
 					iterator tmp = pprev;
@@ -420,6 +432,7 @@ ControlList::thin (double thinning_factor)
 					 */
 
 					pprev = i;
+					prev  = cur;
 					_events.erase (tmp);
 					changed = true;
 					continue;
diff --git a/libs/evoral/evoral/ParameterDescriptor.h b/libs/evoral/evoral/ParameterDescriptor.h
index 33fe4ce70e..824cf24968 100644
--- a/libs/evoral/evoral/ParameterDescriptor.h
+++ b/libs/evoral/evoral/ParameterDescriptor.h
@@ -33,6 +33,11 @@ struct ParameterDescriptor
 		, rangesteps (0)
 	{}
 
+	virtual ~ParameterDescriptor () {}
+	virtual float to_interface (float val, bool rotary = false) const {
+		return (val - lower) / (upper - lower);
+	}
+
 	float normal;      ///< Default value
 	float lower;       ///< Minimum value (in Hz, for frequencies)
 	float upper;       ///< Maximum value (in Hz, for frequencies)