Ask a trombonist how their performance went, and they'll probably first remember how many notes they missed. Terms in the brass player's lingo reflects this concern for accuracy: clam, frak, spleeah, splatter, etc.
The causes for most clams can be traced back simple origins:
INNER HEARING (or the lack of it)
A reasonable argument can be made that most missed notes arise from the simple fact that they weren't clearly heard before they were played. In other words, if the note isn't clear in your mind before you attempt to play it, you are far more likely to miss it. Without this inner hearing, you are playing by feel.
Don't forget the value of sight singing for the development of inner hearing. In fact, even whistling, if done carefully, can be beneficial. (For more on this, see the Feb. 2004 issue of the BoneTalk newsletter in the section, "BoneTips."
If you are fairly good at mouthpiece buzzing and are struggling with accuracy on a high note, try simply buzzing it a few times on the mouthpiece. This exercise forces you to hear the note in your mind and replicate that sound on your mouthpiece without worrying about the mechanics of the instrument.
KEEPING YOUR HOUSE IN ORDER
If you can hear the notes clearly in your head, you have taken a big step towards greater accuracy and consistency. However, without strong fundamentals of technique, you still have your work cut out for you. Look closely at your practice time. How much time is devoted to such relatively mundane tasks as scales, arpeggios and interval work? How much time do you devote to developing clean attacks in the high register? You must lay a strong technical foundation so that, when your ear clearly hears the note, the body is well-trained to consistently produce it.
PRACTICE versus PERFORMANCE
Suppose you are working on an awkward passage in the practice room. On your
tenth try, you "nail it." If you now move on to other material, you have just
taught yourself to miss the passage 9 times out of 10! Once you get it right,
the practicing begins! Teach yourself in the practice room the same kind of
mental intensity you'll use in performance. The adage is old but still has
a lot of truth:
Practice as you would perform. Perform as you would practice.
TRUSTING YOURSELF
Nobody likes to clam a note. Once you have really "splattered" a few notes in front of others, it is easy to start tensing up in anticipation of an approaching high note. Ironically, this act of tensing up makes it all the more likely that you'll miss. Give yourself permission to fail. In other words, go for the note with relaxed mental focus and accept that, if you miss, the world doesn't end.
When you think something like, "Don't miss
that G!", you are thinking about the act of missing the G!
It seems as if word "don't" is dropped from the sentence and all
your muscles hear is, "Miss that G!"
Instead, imagine hitting the note dead center. The more clearly you can imagine
it, the more likely your body will have clear, positive instructions to follow.