Mel频率倒谱系数平滑的耳机均衡

适当均衡耳机到鼓膜的传递函数可有效提高耳机声重放效果。耳廓与耳道滤波效应引起的幅度峰谷有助于人耳听觉感知,以平直幅频响应为目标的幅度均衡无法保持适当的峰谷。该文提出了基于roex滤波器与Mel频率倒谱系数的耳机到鼓膜的传递函数平滑方法,用于模拟人耳听觉感知特性和平滑耳机到鼓膜的传递函数,使均衡后的幅频响应保持相应的峰谷,避免了幅度峰谷过渡均衡。实验结果表明,进行耳机到鼓膜的传递函数平滑的幅度均衡对提高耳机的音色有显著作用,基于Mel频率倒谱系数平滑的幅度均衡对提高耳机的音色最为显著。     

耳道入口处声压分布模态作为听觉方向感知隐性线索的实验分析

通过分析双耳录音与真实听音之间的差别,推断存在影响听觉方向感知的隐性线索,而由头部及外耳结构引起的耳道入口处截面声压分布模态可能是其中一种。首先,通过听音实验利用反证法证明听觉方向感知隐性线索确实存在,并归纳总结出隐性线索的有效作用频段;然后,利用有限元仿真方法计算耳道入口处的声压分布,仿真结果表明耳道入口处声压分布是不均匀的,且分布模态与声源方向有关,从数值仿真的角度验证了耳道入口处截面的声压分布模态携带了声源方向信息,可以作为一种隐性定位线索;仿真计算所得前、后声源方向耳道入口处声压分布模态差异显著的频段与听音实验所得的隐性线索有效频段基本相符,在一定程度上支持耳道入口处声压分布模态是一种方向感知隐性线索的推测。      

相位均衡对耳机重放影响研究*

均衡耳机到鼓膜的传递函数可有效提高耳机声重放效果。通过主客观实验对比研究幅度均衡方法、相位均衡方法和幅度相位同时均衡方法,结果表明相比于幅度均衡,相位均衡对耳机瞬态响应的影响更大：当系统相位为线性时,瞬态响应衰减越快,线性相位对耳机重放提升音色有显著作用;而以平直幅频响应为目标的幅度均衡对提升耳机重放效果有限。     

相位均衡对耳机重放的影响

均衡耳机到鼓膜的传递函数可有效提高耳机声重放效果。通过主客观实验对比研究幅度均衡方法、相位均衡方法和幅度相位同时均衡方法,结果表明相比于幅度均衡,相位均衡对耳机瞬态响应的影响更大:当系统相位为线性时,瞬态响应衰减越快,线性相位对耳机重放提升音色有显著作用;而以平直幅频响应为目标的幅度均衡对提升耳机重放效果有限。     

电动扬声器悬置系统蠕变效应建模

对电动扬声器悬置系统的蠕变效应进行了分数阶建模。通过将标准线性固体模型中的牛顿黏壶替换为分数阶Abel黏壶,提出了悬置系统分数阶标准线性固体力顺模型。使用Klippel扬声器单元电阻抗激光测量系统,测量了2只具有不同橡胶折环的中频扬声器单元的电阻抗和传递函数(振膜输出位移/输入声压),并采用最小二乘法拟合实测曲线,得到了模型参数。通过与已有的考虑蠕变效应的4参数对数模型和标准线性固体模型拟合结果的对比,结果表明:分数阶标准线性固体模型能够准确描述力顺损耗因数随频率的变化规律,对蠕变效应具有更好的模拟精度。      

5.1通路环绕声的耳机虚拟重放

提出了一种改进的5.1通路环绕声的耳机虚拟重放信号处理方法。在对现有的信号处理方法进行分析,指出它会产生不自然主观听觉效果后,通过理论和心理声学实验证明,采用HRTF信号处理、环绕声信号去相关等方法,在克服普通耳机声重放的“头中定位”的缺点、虚拟出多环绕扬声器效果的同时,并未带来新的不自然听觉效果。因此信号处理方法可增加听觉上的包围感,从而改善耳机重放的主观听觉效果。     

采用无耳壳头相关传输函数的虚拟声信号处理

本文提出采用无耳壳、封闭耳道的头相关传输函数（HRTF）进行虚拟声信号处理的方法。理论分析表明，在包含功率均衡的扬声器虚拟声信号处理中，采用无耳壳、封闭耳道的头相关传输函数可有效地减少信号处理函数的谷点，从而减少声重发的音色改变。心理声学的实验结果表明，新处理方法的声像定位与传统的带耳壳、耳道的HRTF处理无显著区别，但音色较后者有所改善。因而新的方法更适合实际的虚拟声信号处理应用。     

分布反馈式光纤激光水听器的声压灵敏度频率响应特性

光纤激光水听器的频率响应曲线会在声压传递函数的谐振频率处出现谐振峰,使水听器的工作频带变窄。研制了一种金属膜片端面增敏结构的分布反馈式(DFB)光纤激光水听器。基于电声类比理论,建立了DFB光纤激光水听器的声压传递函数模型,仿真分析了水听器各结构参数对水听器声压传递函数的影响,实现了水听器结构的优化设计,加工制作了水听器原型样品并进行了实验研究。由实验结果可知,DFB光纤激光水听器在2.5~10kHz频率范围内的平均声压灵敏度为-135.99dB,波动幅度小于±0.6dB,且在16kHz附近出现谐振峰,实验结果与仿真分析结果较好地吻合。该研究对DFB光纤激光水听器的研制具有重要指导意义。     

四阶声低通滤波光纤水听器的声压灵敏度频响特性

对四阶声低通滤波光纤水听器的声压灵敏度频响特性进行了详细的理论和实验研究.在已有的低频集中参量模型中引入了一个机械声阻,用于描述系统的机械损耗,从而得到了改进的声学等效电路.相位频响特性对于光纤水听器的阵列应用非常重要,关系到阵列的波束形成效果,进而影响系统定位、识别与跟踪目标的能力,因此在分析幅度频响特性的同时研究了相位频响特性.仿真分析了各主要参量对声压传递函数的影响,得到了一些对声低通滤波光纤水听器设计具有重要指导意义的结论.实测声压灵敏度频响曲线与仿真结果基本一致,较好地验证了理论分析的正确性.四 关键词： 光纤传感器 光纤水听器 声压灵敏度 低通滤波器     

稳态和动态虚拟听觉重放对近场距离感知的影响*

虚拟听觉重放是研究距离感知的一种重要工具,它可分为传统的稳态虚拟听觉重放和动态虚拟听觉重放。然而,稳态虚拟听觉重放经常会产生头中定位而影响距离感知的判断,从而影响最终的实验结果。过去的实验大多采用稳态虚拟听觉重放,因此其结论也存在较大的争议性结论。本文对比研究稳态和动态的虚拟听觉重放对绝对距离感知效果的影响。实验采用非个性化HRTF进行双耳合成,将分布在水平面0.20 m至1.00 m的七个距离、0°至180°的七个方位角下的信号通过耳机进行虚拟重放。心理声学实验结果表明,在稳态虚拟听觉重放条件下,受试者不同程度地报告了存在头中定位。而动态虚拟听觉重放系统能够利用动态因素,从而产生头外化的听觉感知。统计分析表明动态虚拟听觉重放下的距离感知效果与稳态重放存在明显的差异。由于动态虚拟重放更接近真实声源的感知效果,应选用这种方法作为实验工具。同时,在实际的空间声应用中,也应该采用动态虚拟听觉重放产生不同的距离感知。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.