Vibrato is produced best by a gentle and even action in the throat , not the stomach. A good sound comes from a stable embouchure, a cleanly focused air-stream, support from the stomach, and a relaxed throat and tongue. Intonation Intonation is a product of the relationship of the mouth to the head joint. Flat notes are not deflated pitches. Sharp notes are not inflated or pushed higher.
Flat notes result from the lengthening of the air column at the mouth.
The mouth covers more or moves forward. Flat notes at phrase ends are the result of a collapsing embouchure and tightening throat. Sharp notes result from a shortening of the air column at the mouth. The mouth uncovers more or pulls backwards. Overall intonation is a product of the flute and its scale.