Next morning he stopped me at the elevator and told me it sounded weird and that his headphones were broken.
He said all his music sounded off.
Lo and behold, rare cases where tegretol has been known to cause a semitone lowering perception.
Very hard to diagnose as most people don’t notice, but a lot of research done in Japan on musicians and pitch perfect individuals.
Hopefully he grows out of it but doesn’t seem to bug him.