NON-LINEAR REGENERATION MECHANISMS IN WIND INSTRUMENTS

Domain: Physics
It has been known for some years that the air column of a wind instrument behaves linearly at normal playing levels, the non-linear mechanism which gives rise to harmonics of the radiated sound pressure is contained in the pressure controlled reed which maintains the oscillation. Considerable advances have been made recently in the mathematical formulation of the regenerative mechanism, but these depend for their accurate solution on a quantitative knowledge of the form of the non-linearity. This is not well understood and previous work in this area has been largely confined to the non-linearity of the quasi-static flow through the reed. It has become increasingly clear however that the dynamics of the reed also contribute substantially to the non-linear behaviour, and any complete description must be able to take account of both the dynamics of the reed and the time varying flow through it. By direct observation of both the pressure and flow in the mouthpiece of a brass wind instrument during playing, it has been possible directly to measure the non-linearity at various frequencies and playing levels. Some results of this preliminary investigation are presented and compared to previous work in musical acoustics and speech synthesis.

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