The free buzz is the foundation of every brass player’s mechanical understanding of sound creation.
For starters, blow air between the lips, forming the aperture — the small opening where buzz occurs. Keep your airstream moving forward but do not create a sound yet…
…slowly bring lips together (pierce*) until a buzz is created. For higher tones, the aperture must be smaller and firmer controlling a colder/faster airstream. For lower tones, the aperture must be larger and more relaxed controlling a warmer/slower airstream.
*proper piercing is achieved by flexing your aperture muscles to one central point — your aperture. Do not “clamp” your lips together.
If no buzz happens, do not fret! Place the top lip over the bottom lip and attempt a buzz (almost guaranteed if upper lip is relaxed). You should feel your airstream blowing directly down along your chin. Watch out for slobber!!
Once a buzz like this is well practiced, attempt a free buzz while slowly pulling the bottom lip out to the correct position. If the buzz stops, try again! Over time, your airstream should move to a similar angle as that of your lead pipe.
If you are still having trouble with creating a free buzz, buzz on the mouthpiece and pull the mouthpiece away while maintaining the buzz. This requires vigilant use of a fast air stream. When pulling the mouthpiece away, make sure to keep the air moving!!! Control everything at the aperture.