Current waveguide brass instruments appear to capture the essential features of brass tones [14,15,20,21,60]. The horn itself is well understood up to the bell [6,8,3,7,21]. However, there is apparently no complete theory which describes what happens at the bell exit aperture . For example, nonlinear vortex shedding has been measured downstream from the bell output .
Models for the brass-player's lips are rapidly developing [,18,1,14,46], and there appears to be a trend in the direction of the one- and two-mass models which have been used for years to model the vocal folds in speech . It is clear that the lip model should vary with pitch since the motion of the lips qualitatively changes as the pitch increases [, see Figure 3].