Kunitoshi Motoki

Measurement of sound-pressure distribution in replicas of the oral cavity.

The spatial distributions of sound pressure in artificial oral cavities were measured to examine the characteristics of wave propagation in the vocal tract. The measurement was performed with plaster replicas of the oral cavity, and pure tones were used as the driving signals to obtain both amplitude and phase distributions at varied frequencies. Plane-wave propagation, which has been widely assumed for speech production models, was examined from the measured spatial distributions of sound pressure. Trajectories of media particles and vectorial maps of acoustic intensity, which can be computed from the measured pressure distributions, were also presented to visualize the acoustic field in the oral cavity. The results showed that at certain frequencies there existed points where sound pressure was absolutely zero, with the phase spatially circulating around them. Up to about 4 kHz, except at these certain frequencies, the wave front was almost one-dimensional, though an amplitude gradient was seen in the vertical direction.

Effects of higher‐order modes on sound radiation characteristics at the mouth opening

The influence of higher‐order modes in vocal tracts resulting from the speech radiation process are investigated based on acoustic measurement. Though a real vocal tract has a complicated figuration, a uniform rectangular tube was used as a specimen for the theoretical simplicity of wave propagation. The higher‐order modes were intentionally excited at one end of the tube, and were radiated from the other end of the tube that was mounted flush with a plane baffle surface. Spatial distributions of sound pressure in the vicinity of the radiation region were measured precisely. As the result, the measured distributions of sound pressure show good agreement with those of the well‐known ideal piston model below the first cutoff frequency. Above this frequency, however, quite complicated distributions appear even outside the tube. Distributions of particle velocity and acoustic intensity are also introduced to visualize the acoustic field for higher frequencies. These visualizations suggest that in the case of ...

Area estimation from ARMA analysis based on vocal-tract model

A vocal-tract model with boundary conditions is proposed, and it is shown that the model can be applied to a vocal-tract simulator add an estimation algorithm of vocal-tract shapes. Since our vocal-tract simulator can dynamically synthesize continuous speech with the vocal-fold vibration and the loss factor in the vocal-tract, this simulator can be used as a tool for accurate evaluation of the estimation accuracy of the formants or the characteristics of the vocal-tract. We propose a new method estimating cross-sectional area of vocal-tract from the ARMA parameters, and this method is based on the vocal-tract model and our ARMA estimation algorithms.

FEM simulation of tongue deformation for /i/ with a four‐cube model applied to tagged cine‐MRI data

Roles of extrinsic and intrinsic tongue muscles in the production of vowel /i/ were examined using a finite element method (FEM) applied to the tagged cine‐MRI data. It has been thought that tongue tissue deformation for /i/ is mainly due to the combined actions of the genioglossus muscle bundles advancing the tongue root to elevate the dorsum with a mid‐line grooving. A recent study with the tagging‐MRI revealed earlier, faster and greater tissue deformation at anterior top of the tongue than posterior part during /ei/ production. This result implies the contribution of the intrinsic tongue muscle (transverse anterior) with an independent hydrostat mechanism from that of the genioglossus muscle bundles. In this study, a simple four‐cube model is built to examine the co‐contraction effect of the genioglossus and transverse muscles using using the FEM. The simulation result with the anterior transverse muscle (Ta) showed good agreement with the pattern of the tongue deformation obtained from the tagged‐MRI...

Finite‐element method analysis of acoustic characteristics of the vocal tract with the nasal cavity during phonation of Japanese /a/

For this study, the transfer functions and active sound intensities of a vocal tract model with and without a nasal cavity were computed using a three‐dimensional finite‐element method (FEM). The models were based on vowel data obtained by magnetic resonance imaging (MRI) of the vocal tract with a nasal cavity during phonation of the Japanese /a/. The oral cavity was also coupled with the nasal cavity in a three‐dimensional volume of radiation. Effects of wall impedance were also examined. Coupling of the nasal cavity to the oral cavity indicated the following aspects. Additional peaks appeared below 3 kHz for the lossless condition. However, they disappeared in the simulation for the soft wall condition. The sound energy circulation did not occur in the simulation for the soft wall condition. Regarding effects of the wall boundary condition on the spectral envelope, three‐dimensional simulations confirmed the upward shift of lower formant frequencies. However, disagreement of the formant frequencies betw...

Computation of the acoustic characteristics of vocal-tract models with geometrical perturbation by using higher-order modes

This work presents computational results of sound pressure distributions and transfer characteristics for a large number of vocal-tract models which contain geometrical perturbations. A small change of the vocal-tract shape is regarded as a geometrical perturbation of the axis position of each vocal-tract section. Computation of the acoustic field in the models are performed using higher-order modes. The results indicate that acoustic characteristics in the higher frequencies are highly sensitive to the small change of the vocal-tract shape.

Computation of the acoustic characteristics of simplified vocal-tract models by 3-D finite element method

The acoustic characteristics of vocal-tract models are investigated using a three-dimensional finite element method. Several finite element models are created in order to examine the influence of the simplification of the vocal-tract shapes on the finer acoustic characteristics up to the higher frequencies of around 8 kHz. The simplification takes into account the following aspects: cross-sectional shape, bend, branches of the pyriform fossa and the valleculla, and lip protrusion. The effects of the yielding vocal-tract wall are also studied. The results indicate that with the frequency range up to around the third formant, the simplification of the cross section and the bend is considered to be an effective approximation. It is shown that the use of soft walls suppresses the appearance of sharp peaks and zeros in the frequencies above 3 kHz. It is suggested that the lips and the branches independently affect the shifts of the first three formant frequencies.

Estimation of Sound Pressure Distribution Characteristics in the Vocal Tract

Publisher Summary The characteristics of wave propagation in the vocal tract have been assumed to be those of plane waves because the wavelength of sound in the frequency range of speech is relatively long compared with the cross-section size of the vocal tract. Based on this assumption, a model of the vocal tract is constructed as a cascade of connected uniform tubes having cross-sectional areas corresponding to the predetermined vocal tract area function. This chapter describes the characteristics of the sound pressure distribution in the vocal tract. Since it is very difficult to directly measure the sound pressure distribution in the real vocal tract, plaster replicas were made, which duplicate the actual shapes of the oral cavities, and measured the complex sound pressure distribution. Vectorial maps of active and reactive sound intensity are shown in the chapter. From the vectorial maps, one can see the equi-phase and the equi-amplitude lines in the replicas. From the experimental results, it is shown that the wave front at high frequencies forms a quite complicated curve like a circular pattern, and the assumption of plane wave propagation is not always valid even at low frequencies especially around the tongue tip.

A lattice filter model with accurate lip impedance for dynamic articuratory movement

In the vocal tract model, the area function of vocal tracts is accurately represented by a polynomial function with only a few parameters, and the digital filter realization includes the loss, the accurate lip impedance and the variation of the tract length. We measured the lip impedance using a manikin and pipes set in a baffle, and obtained the reflection coefficient at the lips. From the results of these experiments, we discuss the difference between the measured characteristics and those of a spherical baffle model, and show a method to obtain approximate digital filters for the reflection characteristics at the end of the vocal-tract; i.e. the lips. By introducing this filter, it becomes possible to express arbitrary changes of the length of the vocal-tract without changing the sampling frequency.