Pulsed Noise

A stick-slip event never involves only one bow hair, and during the slipping interval, or string ``flyback,'' there is a soft noise burst which is audible, especially at close range. It is well known that pulsed noise is an important feature of high quality bowed-string synthesis as well as other instruments [1]. The Stick/Slip Bit provided by the bow-string contact model (see Fig. 2) indicates when sliding noise is appropriate. As in the case of the time-varying string-damping discussed above, more refined noise-generation models can be devised based on the bow force, differential velocity, and position information available from the bow-string simulator, as well as an external ``bow angle'' control.

When the resonating body transfer function is factored [5] into slowly decaying modes (implemented parametrically using recursive filters and not necessarily commuted) and rapidly decaying modes (which are commuted and used in nonparametric form as impulse response data), the commuted nonparametric impulse response is qualitatively a short, high-frequency noise burst, since it consists of the impulse responses of thousands of high-frequency, highly damped modes. In principle, this ``damped-modes-noise-burst'' should be convolved with the noise arising from the slipping bow. In other words, the string excitation for each stick-slip event can be modeled as a filtered noise burst which includes both the highly damped resonator modes and the bow noise.