Acoustical study of the playing characteristics of brass wind instruments
Logie, Shona Mary
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When assessing the quality of a brass instrument the player must consider a number of factors, the main consideration being the playability of the chosen instrument. The playability of an instrument is a broad term used to describe how well the instrument plays; this includes how in tune the resonant modes are, how easy it is to start and move between notes, how easy it is to bend notes and the degree of spectral enrichment during a crescendo that is able to be produced. The starting transient is known to be of crucial importance for both the musician and listener, and previous work in the field has been mainly concerned with such starting transients; this work focusses on inter-note transitions. Transitions between notes include both starting and finishing transients as the initial note is ended and the next begun. Using high speed photography images synchronised with pressure signals from the mouthpiece and bell end, the internote transitions are explored. Results from these experiments are compared with those from a simple one dimensional time domain model. Other techniques used to determine the playability of a specific instrument include the rate at which the instrument timbre becomes `brassy' due to nonlinear effects, that are a consequence of loud playing. The relative significance of viscothermal wall losses and nonlinear effects within realistic brass instruments have been explored here using experiments on cylindrical tubes of different internal diameters. These experimental results are compared with results from a computational model that uses weakly nonlinear wave propagation theory and includes viscothermal losses. It is also possible on some brass instruments, when playing loudly, to achieve what are known as super high notes; these notes are above the frequency where the instrument has well defined resonances. Experimental results are presented here using optical techniques to visualise the motion of the player's lips during playing of these super high notes.