Fix some inconsistent usage of a Controllables Interface value.

This breaks a lot of controls, because they are misusing it as well.

libs/ardour/ardour/automation_control.h

@@ -78,18 +78,6 @@ public:
 	void set_value (double);
 	double get_value () const;
 
-	virtual double internal_to_interface (double v) const {
-		return v;
-	}
-	
-	virtual double interface_to_internal (double v) const {
-		return v;
-	}
-
-	virtual double internal_to_user (double v) const {
-		return v;
-	}
-
 	double lower() const { return parameter().min(); }
 	double upper() const { return parameter().max(); }
 	double normal() const { return parameter().normal(); }

libs/ardour/plugin_insert.cc

@@ -1230,24 +1230,13 @@ PluginInsert::PluginControl::set_value (double user_val)
 double
 PluginInsert::PluginControl::internal_to_interface (double val) const
 {
+	val = Controllable::internal_to_interface(val);
+	
 	if (_logarithmic) {
-		/* some plugins have a log-scale range "0.."
-		 * ideally we'd map the range down to infinity somehow :)
-		 *
-		 * one solution could be to use
-		 *   val = exp(lower + log(range) * value);
-		 *   (log(val) - lower) / range)
-		 * This approach would require access to the actual range (ie
-		 * Plugin::ParameterDescriptor) and also require handling
-		 * of unbound ranges..
-		 *
-		 * currently an arbitrarly low number is assumed to represnt
-		 * log(0) as hot-fix solution.
-		 */
 		if (val > 0) {
-			val = log (val);
+			val = pow (val, 1/1.5);
 		} else {
-			val = -8; // ~ -70dB = 20 * log10(exp(-8))
+			val = 0;
 		}
 	}
 
@@ -1258,14 +1247,15 @@ double
 PluginInsert::PluginControl::interface_to_internal (double val) const
 {
 	if (_logarithmic) {
-		if (val <= -8) {
+		if (val <= 0) {
-			/* see note in PluginInsert::PluginControl::internal_to_interface() */
 			val= 0;
 		} else {
-			val = exp (val);
+			val = pow (val, 1.5);
 		}
 	}
 
+	val = Controllable::interface_to_internal(val);
+	
 	return val;
 }