I’m working on Fnugg but am having trouble getting a convincing-sounding E vowel sound, esp when there’s a quick E-O-E. In other words, it sounds more like I don’t know how to do multiphonics rather than a deliberate change in timbre. Also, I’m having difficulty in getting a good slap bass sound w/the lip beat. I can’t seem to do it w/out getting at least a piece of one partial or another. Any suggestions? Syllable changes are getting clearer if you get more lip into the mouthpiece, a more nasal sound. It also has to do with the balance between tubasound and voice. Try less tuba. Practice slow so that you can hear and control the changes.
As you learn it, it will actually improve your regular playing technique as well.