Air stream and the standing wave

The power of the blow (i.e. the excitation or input energy) determines the loudness of the note including crescendos, diminuendos, accents, etc.

The vibration properties of the lips together with the coupling of the instrument determine the pitch. When passing the vibrator, part of the kinetic energy of the air stream transforms into wave motion energy, and part of it continues through the instrument. The former part will make the desired sound, while the latter part is mostly noise (sizzle, hiss, sigh) and useless for good tone production. Too much noise is disturbing and indicates wasted energy. A brass player’s purpose is to produce a full, rich sound - that means great sound/air stream efficiency.