What’s the difference? Predicting and characterising timbral distinctions between families of brass instruments

The distinguishing feature of a brass instrument is that the sound is generated by the vibration of the player’s lips pressed against an entrance hole or mouthpiece. The word “labrosone” (literally “lip-sound”) has been coined as a more scientifically based generic name for a brass instrument. The labrosone class incorporates many families of instruments, each with characteristic distinguishing properties. From the musical point of view, the timbre or tone quality of an instrument is one of its most important features, and timbral differences play a vital role in distinguishing between different families of brass instrument. One particular aspect of timbre – the increase in the brightness of the sound which occurs during a crescendo – is so characteristic of brass instruments that the sound of a very loud and bright note is often described as “brassy”. The generation of brassy timbre by nonlinear sound propagation inside the instrument is described. A brassiness potential parameter, which can be calculated from knowledge of the bore profile, is defined, and its usefulness in characterising the different timbres of different brass families is illustrated. The influence of the absolute radial scale of the instrument is discussed, and several approaches to a more general spectral enrichment parameter are reviewed