Acoustical cues for sound localization by the Mongolian gerbil, Meriones unguiculatus

The present study measured the head-related transfer functions (HRTFs) of the Mongolian gerbil for various sound-source directions, and explored acoustical cues for sound localization that could be available to the animals. The HRTF exhibited spectral notches for frequencies above 25 kHz. The notch frequency varied systematically with source direction, and thereby characterized the source directions well. The frequency dependence of the acoustical axis, the direction for which the HRTF amplitude was maximal, was relatively irregular and inconsistent between ears and animals. The frequency-by-frequency plot of the interaural level difference (ILD) exhibited positive and negative peaks, with maximum values of 30 dB at around 30 kHz. The ILD peak frequency had a relatively irregular spatial distribution, implying a poor sound localization cue. The binaural acoustical axis (the direction with the maximum ILD magnitude) showed relatively orderly clustering around certain frequencies, the pattern being fairly consistent among animals. The interaural time differences (ITDs) were also measured and fell in a +/- 120 micros range. When two different animal postures were compared (i.e., the animal was standing on its hind legs and prone), small but consistent differences were found for the lower rear directions on the HRTF amplitudes, the ILDs, and the ITDs.     

Model-based sound synthesis of the guqin

This paper presents a model-based sound synthesis algorithm for the Chinese plucked string instrument called the guqin. The instrument is fretless, which enables smooth pitch glides from one note to another. A version of the digital waveguide synthesis approach is used, where the string length is time-varying and its energy is scaled properly. A body model filter is placed in cascade with the string model. Flageolet tones are synthesized with the so-called ripple filter structure, which is an FIR comb filter in the delay line of a digital waveguide model. In addition, signal analysis of recorded guqin tones is presented. Friction noise produced by gliding the finger across the soundboard has a harmonic structure and is proportional to the gliding speed. For pressed tones, one end of a vibrating string is terminated either by the nail of the thumb or a fingertip. The tones terminated with a fingertip decay faster than those terminated with a thumb. Guqin tones are slightly inharmonic and they exhibit phantom partials. The synthesis model takes into account these characteristic features of the instrument and is able to reproduce them. The synthesis model will be used for rule based synthesis of guqin music.     

Some roles of the vocal tract in clarinet breath attacks: natural sounds analysis and model-based synthesis

A simplified physical model mainly devoted to the reproduction of some transients of clarinet-like instruments is presented. From time-frequency analyses of natural clarinet sounds, it is shown that the vocal tract can play a significant role in some attacks as well as in the permanent regime. The model proposed consists in supplying a pressure source at the entrance of a cylindrical bore attached to the mouthpiece, allowing one to reach various vocal tract configurations. For real-time synthesis purposes, a digital scheme solving the physical problem is proposed. It is shown that this synthesis model is able to reproduce some of the complex features observed during the attacks of the natural sounds analyzed, as well as known effects of the vocal tract in permanent regime.     

Acoustical analysis and perceptual evaluation of tracheoesophageal prosthetic voice

Voice analysis was performed on 21 “standard” laryngectomized, male patients with a Provox® voice prosthesis, along with an age- and sex-matched control group of 20 normal speakers, using acoustical analyses (MDVP and CSL, Kay Elemetrics Corp.), maximum phonation time measurements, and perceptual evaluations. Comparison between MDVP and CSL revealed that the latter was not useful for the analysis of laryngectomized prosthetic voices. In contrast, MDVP seems suitable for this purpose, and contains a large number of parameters that significantly differentiate between patient and control speakers, as did the perceptual ratings and the maximum phonation time. Fundamental frequency appeared to be comparable for patients and control speakers. A significant influence of stoma occlusion and age was found for some voice parameters. Factor analyses showed correlations between the different MDVP parameters and correlations between the MDVP parameters and the perceptual ratings.     

Acoustical remodeling of a large fan-type auditorium to enhance sound strength and spatial responsiveness for symphonic music

The Grand Theater in the Sejong Performing Arts Center in Seoul, Korea is a proscenium hall with 3022 seats. Originally built in 1978, the Grand Theater was remodeled in 2004 to provide variable reverberation time (RT) using a sound system. Recently, a second remodeling was scheduled to enhance the hall’s acoustic quality, especially its RT, sound strength (G) and binaural quality index (BQI = 1-IACCE3), based on architectural acoustic analysis. In the remodeling plan, the wall covering and chair materials were changed to produce longer RT and higher G. For the remodeling design, side balconies were added to the first and third floors to provide lateral reflections to the audience area. The orchestra shell and various ceiling/wall reflectors were planned to provide more early reflections to the audience area. To verify the design, the effects of these structures on the sound pressure levels and spatial parameters of early sound in the audience area were investigated by open-type 1:10 scale model measurement. In addition, the acoustical qualities of the remodeled hall were evaluated using computer simulations and 1:50 scale model measurement. The results show that G was improved by 5 dB and BQI by 0.24, whereas the occupied RT at mid-frequencies became variable from 1.47 to 2.24 s.     

Acoustical Klein-Gordon equation: a time-independent perturbation analysis

The perturbation analysis of an ideal acoustical duct was first made by Rayleigh in 1878 and the result has since stood in the literature. However, the analysis is based on the assumption of potential and kinetic energy densities that remain constant as a change in cross section occurs, whereas, in fact, they may fluctuate significantly in comparison to the slowly varying "wave function," Psi(x,t), of the acoustical Klein-Gordon equation. The square of the time-independent eigenfunction, psi(2)(x), is directly proportional to the potential energy per unit length of fluid, and it is shown that it is precisely the perturbation in potential energy that defines correctly the eigenvalue shifts.     

Time domain simulation and sound synthesis for the snare drum

The snare drum is a complex system, relying on the interaction of multiple components: the drumheads, or membranes, a set of snares, the surrounding acoustic field and an internal cavity. Because these components are multidimensional, and due to a strong distributed non-linearity (the snare interaction), many techniques used frequently in physical modeling synthesis applications, such as digital waveguides and modal methods are difficult to apply. In this article, finite difference time domain techniques are applied to a full 3D system, and various features of interest, such as the coupling between membranes, and the interaction between the membranes and the snares, are examined in detail. Also discussed are various numerical features, such as spurious splitting of degenerate modes and bandwidth limitation, and estimates of computational complexity are provided. Sound examples are presented.     

阻尼受击板的时域建模及声音合成

为满足声源辨识中对合成冲击声的迫切需求,建立了球-板撞击的时域模型,提出一种时域快速求解方法,并进行了实验验证.首先给出一种将时域有限差分法(FDTD)和模态展开法(MEM)相结合的时域混合方法,求解板的振动方程,并解决了混合方法中MEM的模态截断和初值问题,及两种方法中阻尼的一致性问题;随后,给出了简支矩形板的冲击声计算结果,通过与FDTD方法的运算量进行对比,验证了混合方法的高效性;最后,针对自由边界下的L形板进行了实验验证.结果表明,与传统FDTD方法相比,时域混合方法在保证合成冲击声精度的前提下可将计算效率提高100至1200倍。     

Acoustical analysis of the auditory system of the cricket Teleogryllus commodus (Walker)

The basic auditory physiology of crickets, and particularly of Teleogryllus commodus (Walker) is examined and its behavior simulated by electrical analog networks, beginning from the simplest possible model and progressing by stages to the full system found in the real insect. It is found that the attenuation of sound in the auditory trachea plays a crucial role in the mechanism for directional hearing in even the simplest model and that the tracheal diameter is in fact appropriate to produce the desired attenuation. In a more complex model in which it is recognized that the auditory system probably responds to pressure changes in the tracheal sacs underlying the tympana rather than simply to tympanic motion, it is found that the phase shift produced by the combined effects of the central septum and the adjoining cavities leading to the spiracles is also important to hearing directionality. The final model which includes both tympana and spiracles is able to simulate both the hearing directionality and, in part, the frequency selectivity of the system. It appears, however, that a large measure of the observed frequency selectivity is due to some form of selectivity in the neural transducers themselves rather than in the simple acoustic components of the system.     

Acoustical analysis of pipes with flow using invariant field functions

An analysis of the pressure field within a pipe is carried out using simplified formulations of pipe acoustics. The fluid contained within the pipe is considered non-viscous, while the flow velocity of the fluid is assumed to be smaller than the speed of sound.The analysis is limited to frequencies which are well below the pipe ring frequency, i.e., at which only simple waves can propagate. Expressions and diagrams are given which specify the applicable frequency range in each particular case.Three invariant functions of the internal pressure field are evaluated. These functions allow for the determination of the following quantities: base pressure spectrum (spatial mean r.m.s. value), lower and upper bounds of the pressure spectrum for the entire pipe, pressure spectrum at an arbitrary position, speed of sound in the contained fluid and fluid flow velocity.Experimental identification of these quantities requires simultaneous measurement at three points. A few measurements carried out on one air-filled and one water-filled pipe have demonstrated the potential of pipe invariant functions for acoustical analysis.     

传统笙的物理模型及声音合成方法

为研究传统笙的物理结构与音色之间的关系,提出了传统笙的物理模型及声音合成方法。在簧舌振动模型的基础上,结合指孔和音窗的传输矩阵计算方法,建立了笙管的等效电路,并将二者结合,得到笙的完整物理模型。为了验证模型的有效性,设计了一套笙的实验系统,实现了对笙管发声过程中特征量的多通道同步测量。通过对比实验和模型仿真结果的时频域特点以及与音色相关的特征量,分析了模型的性能.结果表明,该模型可较好地模拟传统笙管的发声过程,合成笙样本能够较准确的反映真实笙样本的音色特征。     

Method for measuring violin sound radiation based on bowed glissandi and its application to sound synthesis

This work presents a method for measuring and computing violin-body directional frequency responses, which are used for violin sound synthesis. The approach is based on a frame-weighted deconvolution of excitation and response signals. The excitation, consisting of bowed glissandi, is measured with piezoelectric transducers built into the bridge. Radiation responses are recorded in an anechoic chamber with multiple microphones placed at different angles around the violin. The proposed deconvolution algorithm computes impulse responses that, when convolved with any source signal (captured with the same transducer), produce a highly realistic violin sound very similar to that of a microphone recording. The use of motion sensors allows for tracking violin movements. Combining this information with the directional responses and using a dynamic convolution algorithm, helps to improve the listening experience by incorporating the violinist motion effect in stereo.     

复杂结构冲击声合成及实验验证

以复杂结构受击振动响应的时域计算为目的, 讨论了结构阻尼的计算方法, 给出一种用于冲击声合成的综合数值方法, 并进行了实验验证. 首先, 考虑到阻尼是影响瞬态振动时变特性的重要因素, 详细讨论了两种模态阻尼的计算方法; 其次, 对阻尼板的受击振动和声辐射进行了时域仿真, 并与时域有限差分法的计算结果进行对比, 显示出两种声音合成方法的计算结果具有高度的一致性; 最后, 针对有限长圆柱壳的受击振动, 将合成声与实验录音进行了对比研究. 结果表明, 合成声与实际录音的时域包络、频谱结构以及衰减趋势基本一致, 证明了采用数值方法进行冲击声合成的有效性. 关键词： 声音合成 模态阻尼 冲击声 数值方法     

Acoustical properties of coal

A model has been proposed for bituminous coal which takes into consideration the transverse isotropic properties of coal and the effects of the nature of fluid in the pores on its acoustical properties. The predicted values were then compared with the experimental results performed on a bituminous coal slab, and good agreement was found between the predicted and experimental values, thus verifying the proposed model. The sound velocity through coal increases and the attenuation decreases as the pores become saturated with water.     

Acoustical holography and its applications

A device capable of producing images of objects immersed in opaque media could find application in such areas as engineering inspection, underwater viewing, and medical diagnosis. The results of some experiments in acoustical holography as a viewing system are presented here, together with an assessment of the problems which must be solved before the technique can find useful application.     

Wavelet and model-based spectral analysis of color doppler optical coherence tomography

Color doppler optical coherence tomography (CD-OCT) uses time-frequency analysis (TFA) to extract motion-induced Doppler shifted in the interferometric OCT signal. In this paper, the performance of three TFAs are compared in a scattering flow phantom and in in vivo human retina: the short-time Fourier transform, the Morlet-wavelet transform, and the short-time MUSIC transform (STMT). The STMT is a new TFA that incorporates the MUSIC eigenfrequency estimator in a generalized short-time framework. The Morlet transform excels at identifying blood vessels, while the STMT is the most accurate predictor of Doppler shift frequency.     

保利剧院的声学设计

保利剧院是一座继承传统歌剧院的良好品质,又能适应近代各种需求的专业歌剧院,兼供自然声音乐演奏和戏剧演出,为确保剧有良好的音质,从方案阶段就开始声学设计,并贯穿于设计、施工、试用调试的全过程,从而获得了良好的音质,评价颇高,本文概要介绍保利剧院的声学设计及从中取得的经验。