Experimental investigations of lip motion in brass instrument playing
Stevenson, Samuel D. F.
The precise nature of the motion of the lips of the musician is critically important to the sound of the brass wind instrument. The player must match the oscillation of the lips to the acoustical properties of the instrument and it can take many years of practice to master the techniques involved. Visualisation techniques for capturing the motion of the lips during performance are described and the behaviour of the lips quantitatively analysed using digital image analysis. The concept of an artificial mouth for the sounding of brass wind instruments is discussed and the motion of the artificial lips is compared to that of human musicians. When a brass instrument is played loudly the energy of the higher harmonics increases, creating a distinctive ‘brassy’ timbre. It has been suggested that saturation or constraint of the lips of the musician during extremely loud playing is responsible for this change in sound. Measurements of the motion of the lips of a number of different musicians on different instruments suggest that the lips are not significantly constrained at any playing dynamic, and that it is the phenomena of nonlinear propagation and shockwave generation that is responsible for the increase in energy of the higher harmonics. It is widely accepted that the starting transient of a musical instrument is of great importance to both listener and musician. Previous studies of brass instruments have focused on the steady-state behaviour of the lip-instrument interaction. Measurements of the motion of the lips have been synchronised with the pressure in the mouthpiece of the instrument and the sound radiated from the bell in order to investigate the transient behaviour of the system during both the starting transient and slurs between notes. Thiswork has been extended to include measurements of the pressure in the mouth of the player during the starting transient, and this information used to recreate realistic transients using an artificial mouth. The transient behaviour of the system is clearly affected by the time delay between the start of the note and the acoustical feedback from the instrument beginning. The information obtained can be used to aid in the creation of accurate computational and physical models of brass wind instruments.