Musicians don't know what they're doing.

They can't effectively describe what they do or how, and so are not necessarily the best teachers, according to researchers Joe Barbenel and his colleagues at Strathclyde University in England in a report in New Scientist magazine.

Musicians themselves, the researchers have been irritated over the years by conflicting advice and musical mythology about how best to play the trumpet. Information, even from first-rate professionals, is contradictory, sometimes self-contradictory.

So the researchers decided to separate a few facts from myths. How much do great musicians know about how they play? Could they accurately describe their performance?

The most blaring issue in trumpet-playing is the amount of force applied to the mouthpiece when blowing notes. Teachers are obsessed by this aspect of performance, and the standard mythology holds that very little pressure is applied when the instrument is played properly, Barbenel reported.

There are even tales of players who could produce the most difficult notes -- double-high Cs of great force -- while playing no-handed a trumpet suspended from the ceiling by a thread. Suspended, the trumpet slips away from the lips when pressure is applied to the mouthpiece.

Recruiting 30 experts and 30 amateurs, Barbenel's group found:

*"Despite our strong expectations that the less-experienced players would use more force, we found no difference between the groups . . . . "

*Not only was strong force used by all players, but in early tests the measuring device in the trumpet was collapsed by forces in excess of 20 pounds on the mouthpiece.

*Professionals could not tell whether amateurs were using great force or little force by looking at photos of them playing.

*The experts could not judge how much force they themselves were using. Judgments by people picking up the instrument for the first time were equally good.