Making a Great Sound September 10 2014
No, this will not be a debate on how much of each lip should be "in" the mouthpiece or what direction you should blow the air. We will merely explore the action by which tightening certain muscles and breathing air out creates a vibration that is then enhanced by your instrument.
What We Hear
What is sound, man...? No but like, what IS sound?
One thing for sure, is that it isn't magic. Effectively, sound is a pressure wave in a fluid. Within the context of this article, it is important to realize that this isn't an "up and down" wave like a plucked string. The wave we're talking about is a periodic alternation between high and low pressure within the air. This is similar to the actual vibration created in the air by the action of the "up and down" wave of a plucked string. The string actually bumps the air away from itself as it moves, creating the sound.
What You Do
For brass, the mechanics are a little more complicated, but not terribly. The most familiar analogy is squealing a balloon by pulling the rubber apart with your fingers as the air rushes out. Your lips, just like the balloon, are acting as a gate for the air. The vibration corresponds to the cycle of air building up and then releasing through the aperture. This happens quite rapidly. The air pressure from your torso pushes against the back of your closed lips, which are holding in the air with a given amount of tension. When the pressure builds up, it forces the lips apart and flows out. This causes the pressure of the air in your mouth to drop, though, making your lips return and close up again since they're still at the same tension. Once they're closed, the pressure builds up again. Fortunately, you don't have to think about exactly how much force apply to your lips or what exact air pressure matches that for a given pitch. You just have to practice and get used to it.
This build up and release action explains many things you may have noticed about how people play. Everything from tone quality to range can be affected by how well you can create a solid pressure vibration.
Players that struggle constantly with their upper register are likely relying too heavily on their mouthpiece to produce the pitch. Even with proper air support, effective lip tension can only be bypassed with the mouthpiece in a limited range. In the normal, middle register, the player is able to force too much of their lip into the opening of the mouthpiece. While this does, in a way, help the lips stay pushed together for the return action of the vibration, it is much harder to control and produces a compromised tone in most cases. As they play higher and higher, they jam the mouthpiece against their face to help, but eventually the combination of poor face strength and mouthpiece pressure isn't enough to balance the air and the notes no longer come out. They just get air with no return action from the lips.
This can happen on the low end, too. As this person starts to go down in their register, they start applying less pressure with their mouthpiece. If they haven't trained their lips to apply the proper pressure in this range, the same thing happens. They will get all air and no return action of the lips to "close the gate" again. The solution, yet again, is to gradually work your register out from the middle range using proper technique of the embouchure. Often, you'll hear instructors say "set your lips for the top note" when you work down into the lower register. Playing a note in your middle register with perfect technique, and then playing an octave down without moving the mouthpiece or shifting your lips around is a common exercise. You are forcing your lips to be the gate without overly relying on the mouthpiece to apply pressure.
If you start with the idea of creating a clean and efficient pressure wave, you can get an idea of how this would affect tone quality. Different situations create different effects. Let's take an example of a "pinched" tone. We see this a lot with young players, but what can actually cause this?
One major concept here is that your throat, tongue, and teeth -- everything in and around your mouth -- create a resonant chamber for the vibration. A clean buzz is resonant, even without your instrument or mouthpiece. This is especially apparent with whistling, which uses a very similar, if not identical, tongue position and throat shape. You can even see how this is affected by making a "SSHHH" sound and opening or closing your throat and moving your tongue into different positions. You'll notice that the pitch changes. The same thing happens when you play your horn. You don't want anything getting in the way of your lip buzz resonating in your mouth. A pinched tone generally comes from something being too "closed off" in your resonant chamber (mouth). First is teeth. If they're too close, they will block your resonance and add some "pinch" to the sound. The same goes for your throat. Closed off throat = closed off sound. Overall, if your resonant chamber is too small for the pitch you're trying to play, it will come out pinched.
Opposite this "pinched" effect is a tone that is too "spread" or has no "center". Often, this can happen if your teeth are too far apart. This tends to start pulling your lips apart, limiting their function on the return portion of the vibration.
It is important to note here, though, that this is all in relation to the pitch you are trying to play. You want to avoid excess shifting and movement, but at the end of the day, each pitch has a very specific set of configurations that will make it work out and sound good. From there, the context of what you are playing may dictate that you deviate from your optimal embouchure in more advanced situations.
What It All Means
No, but really. Practice. The shape and position of your mouth and lips is unique to you. Understanding how it all works just gives you a framework around which you can learn to modify your embouchure. Knowledge doesn't put in the time to build strength, so it's up to you to try things out and experiment with your embouchure in order to make it work optimally. Have someone listen to you, though! Never forget that the sound you hear with your ear several inches away from the side/back of the bell isn't the same as the sound that projects off of a stage to the back of a hall. What may sound "too focused" to you as the player may project wonderfully into the room.