Gary P. Scavone

Numerical simulations of fluid-structure interactions in single-reed mouthpieces

Most single-reed woodwind instrument models rely on a quasistationary approximation to describe the relationship between the volume flow and the pressure difference across the reed channel. Semiempirical models based on the quasistationary approximation are very useful in explaining the fundamental characteristics of this family of instruments such as self-sustained oscillations and threshold of blowing pressure. However, they fail at explaining more complex phenomena associated with the fluid-structure interaction during dynamic flow regimes, such as the transient and steady-state behavior of the system as a function of the mouthpiece geometry. Previous studies have discussed the accuracy of the quasistationary approximation but the amount of literature on the subject is sparse, mainly due to the difficulties involved in the measurement of dynamic flows in channels with an oscillating reed. In this paper, a numerical technique based on the lattice Boltzmann method and a finite difference scheme is proposed in order to investigate the characteristics of fully coupled fluid-structure interaction in single-reed mouthpieces with different channel configurations. Results obtained for a stationary simulation with a static reed agree very well with those predicted by the literature based on the quasistationary approximation. However, simulations carried out for a dynamic regime with an oscillating reed show that the phenomenon associated with flow detachment and reattachment diverges considerably from the theoretical assumptions. Furthermore, in the case of long reed channels, the results obtained for the vena contracta factor are in significant disagreement with those predicted by theory. For short channels, the assumption of constant vena contracta was found to be valid for only 40% of the duty cycle.

Lattice Boltzmann simulations of the acoustic radiation from waveguides

The application of the lattice Boltzmann method to evaluate the far-field normal mode radiation pattern from an unflanged cylindrical waveguide is considered in this paper. The parameters associated with the radiation process such as directivity factor, end correction and reflection coefficient are predicted and compared with the theory of inviscid normal mode radiation derived by Levine and Schwinger. The good agreement found between numerical and analytical results, as well as the ability to intrinsically resolve fluid dynamics and acoustics problems suggests that the lattice Boltzmann approach is a useful tool to predict complex phenomena involving duct acoustics, such as nonlinear dissipation and the interaction between the acoustic field and the presence of a mean flow.

Digital waveguide modeling of woodwind toneholes

Woodwind tonehole parameters measured by Keefe [D. H. Keefe, J. Acoust. Soc. Am. 72, 676–699 (1982); ibid. 88, 35–51 (1990)] are converted to traveling‐wave scattering parameters suitable for digital waveguide implementation. Digital filters are designed to approximate the reflection and transmission transfer functions implied by the Keefe data. The final result is that each tonehole is modeled using a single, first‐order digital filter. The digital waveguide discrete‐time simulation technique requires significantly less computation time than traditional multiconvolution time‐domain methods, without loss of accuracy. The results of a digital waveguide six‐hole flute bore implementation are compared to Keefe (1990), with excellent agreement.

Characterization of woodwind instrument toneholes with the finite element method.

A method is proposed to determine the transfer matrix parameters of a discontinuity in a waveguide with the finite element method (FEM). This is used to characterize open and closed woodwind instrument toneholes and develop expressions for the shunt and series equivalent lengths. Two types of toneholes are characterized: Unflanged toneholes made of thin material, such as found on saxophones and concert flutes, and toneholes drilled through a thick material, such as found on most instruments made of wood. The results are compared with previous tonehole models from the literature. In general, the proposed expressions provide a better fit across a wide range of frequencies and tonehole sizes than previous results. For tall toneholes, the results are in general agreement with previous models. For shorter tonehole heights, some discrepancies from previous results are found that are most important for larger diameter toneholes. Finally, the impact of a main bore taper (conicity) on the characterization of toneholes was investigated and found to be negligible for taper angles common in musical instruments.

Selective attention to the parameters of a physically informed sonic model

Two experiments tested listeners’ ability to attend selectively to the properties of a physical model comprising collisions between multiple independent sound-producing objects. A probe signal paradigm measured attention to two properties—resonant frequency and number of colliding objects. Listeners completed a baseline task measuring absolute sensitivity at each stimulus against a background noise. Subsequently, stimuli served as both cues and targets; cue validity was probabilistic. When cue and target were generated by the same object (Experiment 1), greater detectability occurred with valid cues for both resonant frequency and object number, implying the presence of attentional mechanisms for these properties. When cue and target were generated by different objects (Experiment 2), selective attention persisted for object number but not for resonant frequency.

Analysis/Synthesis of Sounds Generated by Sustained Contact Between Rigid Objects

This paper introduces an analysis/synthesis scheme for the reproduction of sounds generated by sustained contact between rigid bodies. This scheme is rooted in a Source/Filter decomposition of the sound where the filter is described as a set of poles and the source is described as a set of impulses representing the energy transfer between the interacting objects. Compared to single impacts, sustained contact interactions like rolling and sliding make the estimation of the parameters of the Source/Filter model challenging because of two issues. First, the objects are almost continuously interacting. The second is that the source is generally unknown and has therefore to be modeled in a generic way. In an attempt to tackle those issues, the proposed analysis/synthesis scheme combines advanced analysis techniques for the estimation of the filter parameters and a flexible model of the source. It allows the modeling of a wide range of sounds. Examples are presented for objects of various shapes and sizes, rolling or sliding over plates of different materials. In order to demonstrate the versatility of the approach, the system is also considered for the modeling of sounds produced by percussive musical instruments.

Acoustical interaction between vibrating lips, downstream air column, and upstream airways in trombone performance

This paper presents experimental results on the acoustical influence of the vocal tract in trombone performance. The experimental approach makes use of measurements at the interface between the player and instrument, allowing a relative comparison between upstream airways and the downstream air column impedances, as well as an estimation of the phase of the impedance of the upstream and downstream systems. Measurements were conducted over the full traditional range of playing, during sustained tones with varying dynamic, as well as in special effects such as pitch bending. Subjects able to play over the full range demonstrated significant upstream influence in the higher register of the instrument. These players were categorized in two groups according to their ability to control the phase of the upstream impedance and their ability to generate powerful downstream acoustic energy. Sustained tones played with varying dynamics showed a general tendency of a decrease in vocal-tract support with increase in loudness. Although pitch bends did not involve significant upstream influence at f0, results suggest modification of the lip behavior during bending. Vocal-tract tuning at tone transitions was also investigated and found to potentially contribute to slur articulations.

Noise-free haptic interaction with a bowed-string acoustic model

Force-feedback interaction with a bowed string model can suffer critically from noise in the velocity signal derived from differentiating position measurements. To address this problem, we present a model for bowed string interaction based on a position-constraint friction. We validate the proposed model by comparing to previous work using off-line simulations, and show measurements of interaction on haptic hardware. This noise-free excitation signal leads to cleaner string motion than previous models, thereby improving the quality of force and audio synthesis in the presence of noise.

Design of Recursive Digital Filters in Parallel Form by Linearly Constrained Pole Optimization

We present a technique to iteratively optimize poles of a recursive digital filter in parallel form. Only exposing the poles as the variables to optimize, we employ a linearly constrained gradient descent routine in which the numerical estimation of the error gradient involves first obtaining the zeros by projecting the target response over a basis of responses defined by the pole positions at a given step. Example fits are presented for exponentially decaying white noise and measured violin radiativity filters.

Effect of task constraints on the perceptual evaluation of violins

Results from two previous studies that involved free-playing evaluative tasks showed that players are selfconsistent in their preference for violins and tend to agree of what particular qualities they look for in an instrument (in this case, “richness” and “dynamic range”). However, a significant lack of agreement between violinists was observed, likely because diff erent players evaluate the same perceptual attributes in diff erent ways. The present study thus investigated whether there will be more inter-player agreement if musicians evaluate violin richness and dynamic range by playing only certain notes in certain registers. Results showed that the more focused the task, the more self-consistent violinists are and the more they agree with each other. We further examined the evaluation of richness from playing versus listening tasks and observed that players were better able to discriminate between violins in the former than in the latter. Finally, the potential correlation of spectral centroid and tristimulus with violin richness were examined. Results showed that the perception of richness is likely associated with the relative amount of low- and mid-frequency partials in a given sound (i.e., low spectral centroid and high tristimulus 1 and 2), though more exploration would be necessary before drawing any conclusions.