not merged for now by upstream (was for Pitch.h) but definitely required
see https://sourceforge.net/p/rosegarden/bugs/1746/#a512
--- a/src/base/Pitch.cpp
+++ b/src/base/Pitch.cpp
@@ -28,6 +28,8 @@
 
 #include <vector>
 
+#include <QObject>
+
 //dmm This will make everything excruciatingly slow if defined:
 //#define DEBUG_PITCH