The speed of the air is determined by the size of the lip's opening and the pressure produced by the support muscles. The speed of the air stream and its volume are independent variables. The lips control the speed of the air delivered by the support muscles. The amount of air delivered by the support muscles determine the loudness of that sound. Strong low notes come from a dense, clean, focused air stream.
Vibrato is an simple undulation in the air pressure.
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.