Added default value for the speed of sound at 20 degree.

include/ITAConstants.h

@@ -65,6 +65,10 @@ namespace ITAConstants
 
 	static std::vector< float > OCTAVE_CENTER_FREQUENCIES_ISO_F = { 31.5f, 63, 125, 250, 500, 1000, 2000, 4000, 8000, 16000 };
 	static std::vector< double > OCTAVE_CENTER_FREQUENCIES_ISO_D = { 31.5f, 63, 125, 250, 500, 1000, 2000, 4000, 8000, 16000 };
+
+	// Speed of sound 
+	static float SPEED_OF_SOUND_F = 344.0f;
+	static double SPEED_OF_SOUND_D = 344.0f;
 };
 
 #endif // INCLUDE_WATCHER_ITA_CONSTANTS