UNSW Sydney
Abstract :
Players coordinate tongue release and variation in blowing
pressure to produce a range of desired initial transients, e.g. for
accents and sforzando, players use higher pressures at release
to give higher rise rates in the exponential phase. The
mechanisms were studied with high-speed video and acoustic
measurements on human and artificial players of clarinets and
simpler models. The initial mechanical energy of the reed due to
deformation and release by the tongue is quickly lost in
damping by the lip. The varying aperture as the reed moves
towards equilibrium produces proportional variations in flow and
pressure via a mechanism resembling the water hammer in
hydraulics. Superposition of this signal with returning reflections
from the bore give complicated wave shapes with variable
harmonic content. When the reed gain more than
compensates for losses, a nearly exponential phase follows until
the last few oscillations before saturation. Maximal exponential
decay rates (in tongue-stopped staccato notes) agree with
losses measured in the bore impedance spectrum. Including
estimates of the negative reed resistance explains semi-
quantitatively the rise rates for initial transients. Different rates for
higher harmonics contribute to different wave shapes and
spectral envelopes, which are illustrated and modelled here.