My diaphragm breathing is terrible

[Slim]

@scott4

Louis Armstrong is famous for those huge cheeks but he is the only one I ever saw that did this.

Check out Dizzy Gillespie.

[Luke]

You can definitely play high notes quickly just pushing in/out air with your tongue. I can do this easily on holes 7-10 on a C harmonica, for example.

The higher note, the less the diaphragm needs to be engaged, in my experience.