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Singing and playing together helps open and resonate the sound, place the embouchure, and control the air quantity. It can be used as a warm up or extended technique as in Ian Clarke's The Great Train Race (see my performance video of this piece), or in Jazz, as in Roland Kirk!

If you want to beatbox flute like Greg Patillo, this will help. I can't teach you how to beatbox, but this will help you combine your beatbox with the flute!

This technique is also discussed on the second embouchure flexibility video of fluteloophost and in Robert Dick's Tone Development through Extended Techniques.