Spectral Enrichment in Brass Instruments Due to Nonlinear Sound Propagation: a Comparison of Measurements and Predictions

Since the discovery nearly twenty years ago that nonlinear propagation of the internal sound wave in a trombone was primarily responsible for the "brassy" timbre in fortissimo playing, it has become increasingly clear that nonlinear distortion even at moderate sound levels can contribute significantly to the tonal character of a brass instrument. Previous work has explored the effects of bore profile and viscous damping on the rate at which spectral enrichment due to nonlinear distortion develops in brass instruments. This paper reviews evidence from experimental measurements and numerical simulations of nonlinear propagation in brass instruments with different bore shapes and sizes, and discusses the possibility of deriving a quantitative prediction of the relative importance of nonlinear spectral enrichment in a brass instrument from measurements of its bore.