The artificial trombone playing system.

Players of brass instruments know that the position of the tongue is important to the tone and pitch of their instrument, but until recently there has not been a clear explanation. Even unequivocal evidence was hard to come by, because human players tend to control the sound produced by simultaneously varying several variables, including pressure and lip tension.

We provided clear evidence of the influence of the tongue using an artificial trombone playing system. The lips were replaced by a pressure controlled valve, and the player’s vocal tract by a series of models that were modelled on the measured cross sections of the human tract with the tongue in different positions.

Changing from the low tongue to high tongue “vocal tracts”, we observed small but musically significant pitch changes on notes in the same register, and sometimes also changes in playing register. The timbre was also observed to change: the high tongue configuration produced a brighter sound with stronger high harmonics. These changes are similar to those we measured in a study involving professional trombone players from the Sydney Symphony and from other orchestras.

We explain these changes by comparing the high acoustic impedance of the playing resonances of the trombone and the relatively low impedance of the vocal tract — elements that are effectively in series in the playing configuration. Raising the tongue provides an acoustic “horn” that improves the impedance matching between the two.

Sound files illustrating the effect are at http://www.phys.unsw.edu.au/music

Alex Tarnopolsky, John Smith and Joe Wolfe