Michael Krane

Aeroacoustic production of low-frequency unvoiced speech sounds

A theoretical approach to describing unvoiced speech sound production is outlined using the essentials of aerodynamics and aeroacoustics. The focus is on the character and role of nonacoustic air motion in the vocal tract. An idealized picture of speech sound production is presented showing that speech sound production involves the dynamics of a jet flow, characterized by vorticity. A formal expression is developed for the sound production by unsteady airflow in terms of jet vorticity and vocal-tract shape, and a scaling law for the aeroacoustic source power is derived. The generic features of internal jet flows such as those exhibited in speech sound production are discussed, particularly in terms of the vorticity field, and the relevant scales of motion are identified. An approximate description of a jet as a train of vortex rings, useful for sound-field prediction, is described using the scales both of motion and of vocal-tract geometry. It is shown that the aeroacoustic source may be expressed as the convolution of (1) the acoustic source time series due to a single vortex ring with (2) a function describing the arrival of vortex rings in the source region. It is shown that, in general, the characteristics of the aeroacoustic source are determined not only by the strength, spatial distribution, and convection speed of the jet vorticity field, but also the shape of the vocal tract through which the jet flow passes. For turbulent jets, such as those which occur in unvoiced sound production, however, vocal-tract shape is the dominant factor in determining the spectral content of the source.

Unsteady behavior of flow in a scaled-up vocal folds model

Measurements of the fluid flow through a scaled-up model of the human glottis are presented to determine whether glottal flow may be approximated as unsteady. Time- and space-resolved velocity vector fields from digital particle image velocimetry (DPIV) measurements of the flow through the gap between two moving, rigid walls are presented in four cases, over a range of Strouhal numbers: 0.010, 0.018, 0.035, 0.040, corresponding to life-scale f(0) of 30, 58, 109, and 126 Hz, respectively, at a Reynolds number of 8000. It is observed that (1) glottal flow onset is delayed after glottal opening and (2) glottal flow shutoff occurs prior to closure. A comparison between flow through a fully open, nonmoving glottis and that through the moving vocal folds shows a marked difference in spatial structure of the glottal jet. The following features of the flow are seen to exhibit strong dependence on cycle frequency: (a) glottal exit plane velocity, (b) volume flow, (c) vortex shedding rates, and (d) vortex amplitude. Vortex shedding appears to be a factor both in controlling flow resistance and in cycle-to-cycle volume flow variations. All these observations strongly suggest that glottal flow is inherently unsteady.

Reconstruction and Morphometric Analysis of the Nasal Airway of the White-Tailed Deer (Odocoileus virginianus) and Implications Regarding Respiratory and Olfactory Airflow

Compared with other mammals (e.g., primates, rodents, and carnivores), the form and function of the ungulate nasal fossa, in particular the ethmoidal region, has been largely unexplored. Hence, the nasal anatomy of the largest prey species remains far less understood than that of their predators, rendering comparisons and evolutionary context unclear. Of the previous studies of nasal anatomy, none have investigated the detailed anatomy and functional morphology of the white‐tailed deer (Odocoileus virginianus), a species that is ubiquitous throughout North and Central America and in northern regions of South America. Here, nasal form and function is quantitatively investigated in an adult white‐tailed deer using high‐resolution magnetic resonance imaging, combined with anatomical reconstruction and morphometric analysis techniques. The cross‐sectional anatomy of the airway is shown and a three‐dimensional anatomical model of the convoluted nasal fossa is reconstructed from the image data. A detailed morphometric analysis is presented that includes quantitative distributions of airway size and shape (e.g., airway perimeter, cross‐sectional area, surface area) and the functional implications of these data regarding respiratory and olfactory airflow are investigated. The white‐tailed deer is shown to possess a long, double scroll maxilloturbinal that occupies approximately half of the length of the nasal fossa and provides a large surface area for respiratory heat and moisture exchange. The ethmoidal region contains a convoluted arrangement of folded ethmoturbinals that appear to be morphologically distinct from the single and double scroll ethmoturbinals found in most other non‐primates. This complex folding provides a large surface area in the limited space available for chemical sensing, due to the expansive maxilloturbinal. Morphologically, the white‐tailed deer is shown to possess a dorsal meatus that leads to an olfactory recess, a nasal architecture that has been shown in other non‐primate species to cause unique nasal airflow patterns to develop during sniffing that are optimized for odorant delivery to the sensory part of the nose. Additionally, we demonstrate that, during respiration, airflow in the nasal vestibule and the anterior maxilloturbinal region may be transitional or turbulent, in which case turbulent mixing is expected to enhance respiratory heat and moisture exchange, which could be an important contribution to thermoregulation and water conservation in the white‐tailed deer. Anat Rec, 297:2138–2147, 2014.

Correcting for color crosstalk and chromatic aberration in multicolor particle shadow velocimetry

Color crosstalk and chromatic aberration can bias estimates of fluid velocity measured by color particle shadow velocimetry (CPSV), using multicolor illumination and a color camera. This article describes corrections to remove these bias errors, and their evaluation. Color crosstalk removal is demonstrated with linear unmixing. It is also shown that chromatic aberrations may be removed using either scale calibration, or by processing an image illuminated by all colors simultaneously. CPSV measurements of a fully developed turbulent pipe flow of glycerin were conducted. Corrected velocity statistics from these measurements were compared to both single-color PSV and LDV measurements and showed excellent agreement to fourth-order, to well into the viscous sublayer. Recommendations for practical assessment and correction of color aberration and color crosstalk are discussed.

Dynamics of temporal variations in phonatory flowa)

This paper addresses the dynamic relevance of time variations of phonatory airflow, commonly neglected under the quasisteady phonatory flow assumption. In contrast to previous efforts, which relied on direct measurement of glottal impedance, this work uses spatially and temporally resolved measurements of the velocity field to estimate the unsteady and convective acceleration terms in the unsteady Bernoulli equation. Theoretical considerations suggest that phonatory flow is inherently unsteady when two related conditions apply: (1) that the unsteady and convective accelerations are commensurate, and (2) that the inertia of the glottal jet is non-negligible. Acceleration waveforms, computed from experimental data, show that unsteady and convective accelerations to be the same order of magnitude, throughout the cycle, and that the jet flow contributes significantly to the unsteady acceleration. In the middle of the cycle, however, jet inertia is negligible because the convective and unsteady accelerations nearly offset one another in the jet region. These results, consistent with previous findings treating quasisteady phonatory flow, emphasize that unsteady acceleration cannot be neglected during the final stages of the phonation cycle, during which voice sound power and spectral content are largely determined. Furthermore, glottal jet dynamics must be included in any model of phonatory airflow.

Synthesis of unvoiced speech sounds using an aeroacoustic source model

An aeroacoustics‐based method for synthesizing unvoiced speech sounds is presented. The source model is that of Howe (1975) for sound generated by flow of vorticity through a nonuniform duct. In this formulation three quantities must be known: the potential flow velocity, which changes according to the duct shape, the vorticity, and the velocity induced by vorticity in the flow and its images in the duct walls. The potential flow velocity magnitude is found using a transmission‐line representation of the vocal tract, and the direction is found using a panel method. A model for the generation and evolution of vorticity has been developed in which the vortex shedding frequency is a random variable, and the vortex convects at a constant speed and direction. The computational model was used to simulate three cases: (1) a jet flowing through a pipe constriction, (2) a fricative sound (/s/), and (3) a VCV combination (/a s a/). Simulation results are presented and compared to experimental data, in terms of spec...

Synthesis of fricative sounds using an aeroacoustic noise generation model

Results from speech synthesis with an aeroacoustic fricative source model are presented. The source model, which is implemented in the time domain, is based on Howe’s reformulation of the acoustic analogy [Howe, J. Fluid Mech. 71, 625–673 (1975)]. It specifies the source as a function of flow conditions and the geometry of the vocal tract downstream from a constriction where a turbulent jet is formed. This is accomplished by combining elements of aeroacoustic theory and a model for jet behavior with a traditional model for wave propagation in the vocal tract. Using this formulation, the source strength, impedance, and spectrum can be determined through post‐processing. The fricative model is implemented in an articulatory speech synthesizer. Evaluation of the resulting synthesis is emphasized. Comparisons are made with physical experiments in static configurations. Additionally, speech fricatives are compared with natural speech as well as synthetic speech from other models. These comparisons are made in ...

Jet-Supercavity Interaction: Insights from Experiments

An experimental study was performed to evaluate some of the claims of Paryshev (2006) regarding changes to ventilated cavity behavior caused by the interaction of a jet with the cavity closure region. The experiments, conducted in the 1.22m dia. Garfield Thomas Water Tunnel, were performed for EDD to tunnel diameter of 0.022, Fr = 14.5 and 26.2. The model consisted of a converging-section nozzle mounted to the base of a 27.9mm 37° cone cavitator placed on the tunnel centerline at the end of a 138.4mm long streamlined strut. A ventilated cavity was formed over the model, then an air jet, issuing from a converging nozzle, was initiated. Changes to cavity behavior were quantified in terms of cavitation number, thrust-to- drag ratio, and stagnation pressure ratio at the jet nozzle. The results show that, while the overall trends predicted by Paryshev were observed, the data did not fully collapse, suggesting that many of the effects neglected by Paryshevs model have measureable effect.

Multicolor particle shadow accelerometry

This paper describes the extension of multicolor particle shadow velocimetry (CPSV) to the measurement of local acceleration in an Eulerian frame of reference. A validation experiment was conducted on a pendulous disk undergoing unsteady rigid body rotation. Angular velocity and acceleration profiles by CPSA are presented along with a comparison to recordings by an accelerometer mounted on the pendulum. CPSA is also demonstrated in a fully-developed turbulent pipe flow. Profiles of standard deviation of the local acceleration in the near wall region (0< y + <75) are compared to similar measurements by Christensen and Adrian. A favorable comparison is found between CPSA and particle image accelerometry (PIA). The effect of acceleration time delay, or the time between two velocity estimates, on local acceleration estimates is discussed.

Jet-Supercavity Interaction: Insights from Physics Analysis

Various closure conditions of a ventilated cavity enveloping all or part of a high-speed underwater body are introduced, including those involving a propulsion jet. The flow regimes for the latter are described based on Efros-Paryshev theory, which is extended to estimate the efficiency and fundamental limitations of a rocket-type propulsor.