QUOTE(stevensfo @ Jan 17 2007, 08:40 PM)

I'm confused. If playing solo or with other Bb instruments, there's no need to transpose at all. Just play what's written! The trumpet is hundreds of years old and other instruments often have to accommodate. I play in a wind orchestra where it's the poor old flutes who have to fit in with the Bb brass, clarinets etc. In ensemble music the trumpet part will be written in the key already transposed.
You are thinking that there are transposing instruments. A better way to think of it is that on any instrument you could have transposing players or concert pitch players.
This is well illustrated by the euphonium. In the brass band, the player reads from a Bb treble clef part and the note comes out a major ninth lower. In the orchestra (on the same instrument, but now called tenor tuba), the player reads from bass clef, concert pitch.
Bass tubas come in several different lengths, but orchestral tuba parts are always concert pitch.*
Players relate the written notes to the fingering on the instrument they choose, built in F, Eb, C or Bb. In the brass band, Bb bass players have a treble clef transposing part; Eb bass players usually have a bass clef concert pitch part (often named "Bombardon"), and if they were brought up on treble clef can use the trick of adding three sharps and pretending that it is treble.
*without even the octave transposition that the double bass gets from having played from the same part as the 'cellos for 300 years, so orchestral tuba players become expert at reading leger lines a long way below the stave.