 As with the natural trumpet and bugle, the tube trumpet is a simple (valveless) brass instrument, and is therefore in principle limited to a single harmonic sequence, though by employing embouchure it can be made to produce a chromatic scale in the higher registers.It can be constructed in any desired key depending on the length of tubing used; and a working tube trumpet can be retuned to a sharper pitch by trimming the hose.Once shortened it cannot be returned to its original or a flatter pitch.