Motion of the lips of brass players during extremely loud playing

When a brass instrument is played loudly, the energy level of the higher harmonics increases dramatically. The generally accepted explanation for this is non-linear steepening of the wavefront and generation of shock waves within the instrument bore. However, it has also been suggested that changes in the player's lip vibration could play a role in generating this "brassy" sound. To test this hypothesis, the dependence of lip opening-area on time has been measured for different dynamic levels in trombones and horns. Results suggest that the behavior of the open area does not change dramatically when the instrument enters the brassy regime.