How does James Galway produce his vibrato?

My vibrato is "normal" I guess. Not too fast or slow, deep or shallow, faster in the upper register and slower in the lower register. A perfect example of my vibrato would be Patrick Gallois. Galway's vibrato is fast, but it also very deep, and there is a crispness about it that I can't describe. When i try to match his SPEED, my vibrato sound kind of robotic and like trembling rather than vibrato. When I try to match his DEPTH, my vibrato is too slow. He said that vibrato comes from the diaphragm, but a lot of it comes from somewhere in the back of the throat. I also combine both, but when I try to do vibrato with his speed and depth, I go into these kind of multiphonics for some reason. Patrick Gallois' vibrato is beautiful, but I prefer Galway's.