敲击水杯音调变化的实验研究

敲击装水的杯子时音调会发生变化,装水量的多少与音调变化之间的关系已有说明和讨论,但是在对其原因的分析却存在分歧.本文利用虚拟仪器,通过一系列实验,应用具体数据进行了定性分析.实验表明敲击杯口和杯壁,音调变化不同;敲击杯壁不同位置,音调不变.笔者发现从实证的角度得出的结论与以往观点不能完全吻合,从而尝试从杯子的横向、纵向振动、液体的黏滞性对杯子振动的影响等方面来进行解释.     

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     

“水杯编钟”之振源及音程研究

通过实验证实对"水杯编钟"纵敲杯口、横敲杯壁时,分别是空气柱和杯体发声.查找出了部分文献认为纵敲杯口和横敲杯壁发声相同的这一不适结论的原因是模型错误和测量方法不同.实验还表明"水杯编钟"构成8度音程问题并非如通常认为的不能实现或很难实现.     

锥形镀膜光纤探针中飞秒激光脉冲的传输

采用三维时域有限差分法对飞秒激光脉冲照明下锥形镀膜光纤探针内的光场进行了计算,研究了飞秒脉冲在探针中传输时的时域、频谱和相位特性,并分析了不同锥角和不同长度的探针对这些特性的影响.研究结果发现飞秒脉冲在探针中传输时出现了脉冲展宽、幅值振荡以及频谱分裂等现象,并且利用频谱和相位的变化特性初步解释了脉冲的展宽和脉冲振幅随时间周期性变化等现象. 关键词： 时域有限差分法 飞秒脉冲 光纤探针     

超短脉冲激光经透射型体Bragg光栅的时域特性

利用Kogelnik耦合波理论对超短脉冲激光经透射型体Bragg光栅的时域衍射特性进行了研究,讨论了透射型体Bragg光栅的群延迟色散和光栅结构参数之间的关系,分析了群延迟色散和频谱剪切对衍射脉冲时域强度分布的影响.结果表明:当入射超短脉冲脉宽为100fs时,经透射型体Bragg光栅衍射后的脉冲展宽主要源自光栅对入射脉冲的频谱剪切,当入射超短脉冲脉宽为10fs时,衍射脉冲的展宽量不仅受频谱剪切的影响,而且与光栅的群延迟色散密切相关.     

敲击乐器弦振动的Matlab可视化模拟

敲击乐器能够演奏出优美动听的音调旋律,其敲击工具与弦振动之间存在着规律性数理关系,不同形状的锤击工具,产生的音调具有明显差异.利用数理方法推导出敲击乐器采用不同锤击工具(平面锤、余弦凸面锤、细棒锤)产生的弦振动波动方程,通过计算软件Matlad)实现对弦振动复杂的波动方程数值求解,以直观的图像形式对弦振动进行了可视化仿真模拟.     

重复短声的音调辨别阈与信号时程的关系

当重复频率为250,500或1000赫的重复短声信号的时程短于T时,重复短声的音调辨别閾△f_r与信号时程t的平方根成反比,即△f_r=C(T/t)~(1/2).当信号时程长于T时,重复短声的音调辨别閾即恒定在最低的水平,即△f_r=C.T是信息积累的极限时间,较为恒定,约为140毫秒.C为音调辨别閾的最低水平,其大小随受试者的不同及重复短声重复频率的不同而变化.     

基于泽尼克多项式进行面形误差拟合的频域分析

获得泽尼克多项式的频谱信息是正确利用该多项式进行误差拟合的关键。推导出了泽尼克多项式的傅里叶变换公式,在频域中分析了不同阶数该多项式的径向频谱信息和幅角频谱信息,得到了有限项泽尼克多项式能够有效表达面形误差的最大径向空间频率和角频率。基于频域分析理论,利用泽尼克多项式对不同口径局部误差进行了拟合,并利用齐戈（Zygo）干涉仪对带有不同面形误差的光学元件进行了试验分析。结果表明,当误差的径向空间频率或角频率超出泽尼克多项式所能表达的频谱范围时,拟合误差迅速变大。     

θ调制空间伪彩色编码

正1主要内容θ调制是阿贝成像原理的应用:对图像中不同待编色部分赋予不同取向的光栅,制成光栅片.用白光照射该光栅片,在频谱面上得到多列方向不同但0级重合的彩色频谱.如果在频谱面上放置空间滤波器,让不同方向的衍射斑分别透过不同的颜色,就能在像面上得到彩色像.这是利用不同方向的光栅对图像频谱进行调制,因此称为θ调制法.又因为它将图像的不同部位"编"上了不同的颜色,故又称空间伪彩色编码.     

基于滤波成像的大视角数字全息技术

为提高数字全息再现像视角,提出一种基于滤波成像的数字全息技术来实现大视角的三维物体面型测量.利用离轴像面数字全息技术,通过在4F相干图像处理系统的空间频谱面处放置可移动的低通滤波器,使满足CCD分辨率的物光波与参考光波干涉形成全息图,并控制低通滤波及成像区域分别记录不同谱段的子全息图.再现时,首先对子全息图进行数字傅里叶变换,重构对应频谱段,并对频谱段进行拼接形成完整的物光频谱|而后通过数字再现获得大视角的数字全息再现像.利用该方法测量了圆柱形表面（光滑的缝纫针）的三维形貌,并取得了较好的实验结果.     

Pitch and pitch discrimination of broadband signals with rippled power spectra

A random-interval pulse train or wide-band noise when delayed (tau) and added back to itself (cos+) produces a stimulus with a consinusoidally varying (or trippled) power spectrum. The spacing between the peaks in the spectrum is equal to the reciprocal of the delay (1/tau). If the stimulus is delayed and added back at 180 degrees phase reversal (cos-), then a cosinusoidally varying power spectrum is generated whose spectral peaks are separated by 1/tau, but whose peaks are displaced by 1/2tau relative to the power spectrum of the cos+ stimulus generated with the same day, tau. These stimuli yield a pitch, such that the pitch of the cos+ stimulus is equal to approximately 1/tau and the pitches of the cos- stimuli are equal to approximately 0.9/tau and 1.1/tau. These pitch matching results were studied using a variety of matching stimuli and conditions. Following the identification of the pitches, a method of limits and a same-different procedure were used to study the pitch discriminability of both the cos+ and cos- stimuli. Delays (tau) ranging from 1 to 10 ms were studied covering a pitch range of 90-1100 Hz. The pitch discriminations associated with the cos+ and cos- stimuli were essentially the same for both the random-interval pulse train and the wide-band stimuli. These pitch-discrimination results are compared to those associated with a periodic pulse train. The research is also discussed in terms of discriminations of delayed sounds in reverberant environments. These are consistent with assumptions concerning the autocorrelation of the rippled stimuli within the dominant frequency region for pitch perception.     

中华和钟之双音鎛钟的声频特征和振动方式研究

本文对中华和种之中央Bo钟的声频特性和振动方式进行了研究。利用谱对其辐射声信号进行了谱分析;利用时频分析,研究了其谱结构随时间变化情况;为了了解其频率变化及音高情况,计算了其不同时刻的瞬时平均频率。同时,通过不同位置的振动信号谱分析,重建了其在不同频率下的振动方式。     

A central spectrum theory of binaural processing. The binaural edge pitch revisited

Recently, Klein and Hartmann [J. Acoust. Soc. Am. 70, 51-61 (1981)] investigated a new dichotic pitch, called the binaural edge pitch (BEP). They used computer-generated periodic noise signals to generate BEP. In the study presented here, the BEP is investigated in order to evaluate the predictions of the central spectrum theory with regard to this stimulus. Pitch-matching experiments using a nonperiodic BEP stimulus, produced by means of a modulation technique, led to the conclusion that the strongest pitch sensation in the BEP has the character of a weak fluctuating pure tones in noise, which corresponds to a frequency, equal or almost equal to the frequency of the phase transition. This result fits in with the predictions of the central spectrum theory, which, for instance, does not need the assumption of central lateral inhibition for explaining this pitch. Furthermore, it is shown that this theory can also predict the results obtained in lateralization measurements and BMLD measurements using BEP stimuli as well as related stimuli. The results are compared with the data obtained by Klein and Hartmann.     

Coherence Volume of an Optical Wave Field with Broad Frequency and Angular Spectra

We consider the sizes of a region in a three-dimensional space in which an optical wave field excites mutually coherent perturbations. We discuss the conditions under which the length of this region along the direction of propagation of the wave field and, correspondingly, its volume are determined either by the width of the frequency spectrum of the field or by the width of its angular spectrum, or by the parameters of these spectra simultaneously. We obtain expressions for estimating extremely small values of the coherence volume of the fields with a broad frequency spectrum and an extremely broad angular spectrum. Using the notion of instantaneous speckle-modulation of the wave field, we give a physical interpretation to the occurrence of a limited coherence volume of the field. The length of the spatiotemporal coherence region in which mutually coherent perturbations occur at different times is determined. The coherence volume of a wave field that illuminates an object in high-resolution microscopy with frequency broadband light is considered. The conditions for the dominant influence of the angular or frequency spectra on the longitudinal length of the coherence region are given, and the conditions for the influence of the frequency spectrum width on the transverse coherence of the wave field are examined. We show that, when using fields with broad and ultrabroad spectra in high-resolution microscopy, this influence should be taken into account.     

二维多丝室探测器读出方法的优化

中国散裂中子源将建设一台基于~3He气体的二维多丝室,作为多功能反射谱仪束线的中子探测器.基于已有的研究,为优化选择二维多丝室探测器的丝结构,本文研究了三种不同的丝结构,并采用重心读出方法和数字读出方法进行了探测器的性能测量,得到了满足多功能反射谱仪探测器需求的读出方法.实验结果表明:对同种丝结构的二维多丝室探测器,重心读出方法的位置分辨和成像性能都好于数字读出方法;基于重心法读出的多丝室探测器位置分辨率可以达到约160μm,基于数字读出方法的多丝室探测器位置分辨率可以达到约400μm.优化设计的丝结构为:基于重心读出法的阳极丝间距1.5 mm、读出通道间距4 mm,基于数字读出法的阳极丝间距1.5 mm、读出通道间距2 mm.优化设计的丝结构均能满足谱仪的位置分辨要求.     

A central spectrum model: a synthesis of auditory-nerve timing and place cues in monaural communication of frequency spectrum

A probabilistic psychophysical model for monaural communication from the auditory nerve to the brain is given in the form of a tonotopic display of stimulus spectrum, termed central spectrum. The model builds upon prior research demonstrating the potential of neural timing cues from the auditory nerve for conveying information on complex spectra, and was designed to meet the quantified demands of the psychophysics of frequency measurement. The central spectrum magnitude at each frequency is determined by the response of the auditory-nerve fibre with characteristic frequency matching that frequency. An interval histogram from each fiber is passed through a filter matched to the characteristic frequency of the fiber. This output versus characteristic frequency defines the central spectrum. Detailed analysis demonstrates that efficient probabilistic processing of the central spectrum described known psychophysical properties of frequency measurement in discrimination and periodicity pitch experiments. Psychophysical models based upon the central spectrum model followed by optimum probabilistic pattern recognition are potentially relevant for predicting human communication limits in response to arbitrary sounds of speech and music.     

傅里叶望远镜重构图像虚像分析

研究了采用T型激光发射阵列情况下傅里叶望远镜重构图像的虚像问题, 基于系统成像基本原理, 明确了虚像的来源. 分析认为, 发射光束在x和y轴扫描时, 在俯仰角误差的作用下, 抽取目标的空间频率和设定值之间存在一定的偏差; 当进行轴向和象限相位闭合、计算目标的单一傅里叶分量时, 该偏差会对频谱的频移造成随机的相位影响, 反映在空域上使得重构图像存在虚影现象. 在不同扫描方式情况下, 采用下一步外场实验参数, 通过计算机模拟证实了上述分析的正确性.     

Frequency discrimination near the spectral edge of simultaneous and forward maskers

The effects of the presence of an amplitude discontinuity in the spectrum of a noise masker on frequency discrimination performance were examined. First, detection thresholds as a function of masker level were obtained for pure-tone signals masked by either simultaneous or forward white and low-pass maskers. Then frequency discrimination thresholds were obtained using four masker levels that were chosen to yield predetermined masked thresholds, with signal levels corresponding to each of three sensation levels above these masked thresholds. The principal results indicate that frequency discrimination is poorer in simultaneous low-pass noise than in simultaneous white noise, and that this difference in performance increases with increasing sensation level and with increasing masker level. These results are inconsistent with an explanation based on the pitches generated at spectral edges ("edge pitch"), pitch shifts, or disruption of phase-locking information, but are generally consistent with an explanation based on lateral suppression. It is proposed that a release from suppression may occur in filtered noise backgrounds at high noise levels and at high sensation levels. The reduced suppression may result in poorer frequency discrimination due, in part, to reduced signal detectability.     

Gender recognition from vocal source

Efficiency of automatic recognition of male and female voices based on solving the inverse problem for glottis area dynamics and for waveform of the glottal airflow volume velocity pulse is studied. The inverse problem is regularized through the use of analytical models of the voice excitation pulse and of the dynamics of the glottis area, as well as the model of one-dimensional glottal airflow. Parameters of these models and spectral parameters of the volume velocity pulse are considered. The following parameters are found to be most promising: the instant of maximum glottis area, the maximum derivative of the area, the slope of the spectrum of the glottal airflow volume velocity pulse, the amplitude ratios of harmonics of this spectrum, and the pitch. On the plane of the first two main components in the space of these parameters, an almost twofold decrease in the classification error relative to that for the pitch alone is attained. The male voice recognition probability is found to be 94.7%, and the female voice recognition probability is 95.9%.     

Intensity fluctuations of ultrasonic scattering in a highly turbulent flow

Aspects of ultrasound intensity fluctuations backscattered from additive microstructures in a turbulent flow have been investigated theoretically and experimentally for the conditions of a small insonified volume, a high sound frequency and strong turbulence. These conditions are typically found in high resolution Doppler sonar applications. An easily applicable expression for the auto-correlation of scattering intensity fluctuations is obtained by introducing open-channel turbulence theory, a semi-empirical scalar spectrum (including a Batchelor spectrum) and a Gaussian window function. Experiments carried out in a laboratory-clear water, open-channel flow for different turbulence levels verify the underlying assumptions. A good agreement is found with the predictions made with the above-derived expression. The feasibility of extracting flow information from the backscattered intensity fluctuations is discussed.