乐音音形的感知与谐和性分析

针对乐音的谐和性问题,以听觉与视觉之间的通感现象为基础,从听音联想的角度将"音形"定义为听到乐音时主观联想到的图形。在保证乐音信号等声压级的前提下,通过乐音音形的感知实验和谐和性评价实验,类比视觉审美法则,探索感知音形与听觉谐和性之间的关系。实验及分析结果显示,乐音的感知音形呈现一定的规律性,且感知音形与乐音谐和性评价之间相互关联。乐器单音音形多被感知为单一图形,音程的感知音形多由两个图形组成,且这两个图形分别对应于构成音程的两个单音的感知音形。乐器单音及音程的感知音形与听感谐和性之间存在四种关系,分别是一致、比例、对称和对比融合。     

改进型SPWM调制下的整流器参数设计与仿真研究

针对整流器在电网谐波补偿上受主参数影响变化较大,且在调制过程中易产生高次谐波和非线性等问题,以三相电压型PWM整流器为研究对象,提出了一种按照抑制电流谐波要求设计交流电感和依据直流电压对跟随性、抗扰性要求设计直流电容的方法,并对整定后的电感、电容参数在影响补偿性能方面进行了讨论。在整流器的控制策略上提出了一种动态调节的改进型SPWM算法,在SPWM算法中针对调制度的变化量对采样到的信号进行变换,通过DSP实现脉冲的动态调制。在Matlab/Simulink中对系统进行了仿真研究,结果表明系统参数设计和调制方法稳定可靠,动静态性能良好。     

乘法模型下西洋乐器音色特征

基于乐音的乘法模型分析研究了可用于西洋乐器音色识别的声学特征：谐波能量比、倒谱与Mel倒谱系数（MFCC）和该文提出的机制声MFCC。对西洋管弦乐器的单音进行了特征提取,通过分析乐器特征的模式,评价它们与音色的关联程度。音色由激励源和共振体共同决定,与共振体特性相比,激励源的特征更能反映音色的不同。研究结果表明：强调激励源本质的机制声MFCC和乐音MFCC能更好地体现音色之间的不同;机制声MFCC尤其适合对乐器大类的识别;谐波能量比仅反映共振体特性,可以在一定程度上反映音色的差别;复倒谱与实倒谱区别不同乐器的能力有限。     

低频噪声主观感知与频谱特征关系研究

低频噪声对人的主观影响越来越引起人们的重视,本文采用正交分析方法,研究了低频噪声频谱中不同频率下降点,不同下降斜率,不同频率调制因子和用于调制信号的窄带噪声不同截止频率四个因素对主观低沉度、有调感、粗糙感和烦恼度的影响.主观评价采用了分组成对比较法和参考语义细分法.研究结果表明,不同频率调制因子对粗糙感的影响较大.不同截止频率对有调感和低沉度的影响比较明显.在进行主观烦恼度的统计分析时,需要考虑人群分类的影响,对于不同的人群烦恼度的影响因素会有所不同.     

应用Hilbert变换和ZFFT提取变速器齿轮故障特征

变速器故障齿轮振动信号,调幅现象和调频现象同时存在,其频谱中包括啮合频率及其谐波、调制产生的耦合频率。Hilbert变换无法提供足够高的频率分辨率解调低频调制信号,为此提出复调制细化谱分析方法。通过变速器齿轮故障模拟实验,采集齿轮正常、轻微磨损和严重磨损时的稳态振动信号,对其进行Hilbert变换得到信号的包络,对包络信号进行复调制细化谱分析,得到齿轮轴转频基波及其谐波幅值。随着齿轮磨损程度的增加,齿轮轴转频基波及其谐波幅值明显增大,可作为齿轮磨损故障特征参数。     

基于非线性弹簧模型的振动声调制机理研究

飞机结构裂纹的在线监测是保证飞行器安全的重要举措,针对目前常规的无损检测方法无法实现在线及原位监测的不足,根据裂纹引起的超声非线性,基于振动声调制效应对结构裂纹进行监测是一种可行的方法。采用非线性弹簧模型对裂纹进行模拟,建立了两列一维简谐波在含接触界面的结构中的传播模型,通过公式推导,得到了透射信号的基波、调制边频谐波和高次谐波等信号成分的近似表达式,分析了各谐波成分幅值与激励信号参数间的对应关系,推导了边频调制谐波与两低频基波幅值乘积之比R与刚度系数间的关系。通过板中的振动声调制试验,分析了响应信号的谐波成分及各谐波成分随低频振动幅值的变化关系,探讨了指标R随外力变化情况,试验结果基本符合模型推导的结论,为采用基于振动声调制的方法进行裂纹监测提供了理论指导。     

有理数谐波锁模SOA光纤环形激光器数值研究

采用自再现理论,对工作在有理数谐波锁模时的半导体光放大器(SOA)光纤环形激光器进行了研究.为了获得振幅均衡的有理数谐波锁模脉冲,必须在原有的实验装置中添加一个掺铒光纤放大器(EDFA)以提高注入调制光信号功率.数值结果表明,调制SOA的偏置电流和注入调制光信号功率对有理数谐波锁模脉冲的振幅均衡度都存在较大影响.合理选择调制SOA的偏置电流和注入调制光信号功率,可获得2～5阶振幅均衡的有理数谐波锁模脉冲序列.     

AudioMan:环境信息映射方案的设计与实现

提出了一种电子行走辅助（ETA）系统模型——AudioMan用于辅助盲人行走,盲人用户通过它的声音提示,来判断当前环境的情况。基于可听化技术、听标和耳标,构建了ETA设计中的关键部分——环境信息映射方案。提出了纯音频率、纯音方位、乐音节奏、乐音方位这四套主要方案,制作了原型系统,并对以上方案进行了测试和评估。     

潜力无限的数字混响效果器——调制混响器（1）

现在算法混响和采样混响效果器俨然可以达到过去无法想象的悦耳逼真的混响声。而基于声音调制合成技术的混响效果器——调制混响器的出现,颠覆了传统的混响器反射声建立方式,将控制功能强大的合成调制功能引入到混响器的设计当中。通过强大的路由功能,实现对混响器效果及效果器本身的控制。通过对IK Multimedia CSR-1调制混响效果与传统顶级混响效果器的功能及听感比较,展望今后混响效果器的发展方向。     

基于长度可调T形光声腔和掺铒光纤激光器的光声光谱气体浓度测量系统

应用光声光谱原理设计了气体浓度测量系统。针对C2H2气体运用了掺铒光纤激光器作为光源。光声腔为新型长度可调T形一阶纵向共振式光声腔,调制频率为1099 Hz。将成熟的二次谐波检测技术作为信号处理的基本原理,采用三角波调制并得到受调制后光源输出信号曲线。将二次谐波系数与一次谐波系数的比值作为系统输出,并得到影响其因素的曲线关系。对不同浓度的乙炔气体的实验结果表明,该系统的检测灵敏度为9.634×10^-6,信噪比为41.52 dB。     

Electron trajectory control of odd and even order harmonics in high harmonic generation using an orthogonally polarised second harmonic field

We investigate quantum trajectory control in high-order harmonic generation using an additional orthogonally polarised second harmonic field. By controlling the relative phase between this field and the fundamental, we are able to suppress and enhance particular electron trajectories which results in a modulation of the harmonic emission. We observe a phase shift of the modulation between the short and long trajectories that is different for adjacent odd and even harmonics. These results show qualitative agreement with a full propagation calculation where the single atom response was obtained from the strong field approximation and the main results are explained by consideration of a single atom quantum orbit picture.     

Determination of water vapor by microwave spectroscopy withapplication to quality control of natural gas

The design and construction of a microwave spectrometer is reported. The aim of this instrument is to detect water vapor at low levels. Sinusoidal Stark field modulation is used in order to amplitude modulate the absorption of microwave energy by the water molecule, thus enhancing the sensitivity of the instrument. A semiconfocal Fabry-Perot resonator is used to hold the sample under test. The fourth harmonic of the Stark modulation frequency was used to show the quantitative presence of water in the sample gas. Both atmospheric air, and liquified natural gas (LNG) were used as carrier gases. The peak-to-peak intensity of the fourth harmonic was used to calibrate the instrument against different amounts of water present in atmospheric air. The observed limit of this prototype is around 300 p.p.m. water. No attempt was made to lower the detection limit at this point since the aim of this project was to examine the feasibility of using the fourth harmonic to determine water content reliably     

Wavelength- and amplitude-modulated photoacoustics: comparison of simulated and measured spectra of higher harmonics

Photoacoustic (PA) spectra generated by current modulation of a distributed feedback diode laser (DFB-DL) were measured for the ammonia absorption line at 1.53 microm and calculated using absorption spectra taken from a database. The algorithm is based on a combined amplitude- and wavelength-modulation (AM-WM) scheme. The spectral characteristics of the DFB-DL were determined by comparing simulated spectra with Fourier transform infrared measurements. PA spectra were measured and simulated from the first to fourth harmonic and a variation of the modulation depth with modulation frequency was observed. It was found that combined AM-WM modulation may produce larger PA signals than separate AM or WM detection for the first harmonic.     

Numerical studies on time-domain responses of on-off-keyed modulated optical signals through a dense fog

We present a numerical technique to simulate the propagation characteristics of an on-off-keyed modulated optical signal through fog. The on-off-keyed modulated light (a square wave) is decomposed into a finite number of harmonic components, and a numerical solution for the vector radiative transfer equation is obtained for each harmonic that corresponds to the modulation frequency. With this method we study the distortion and the pulse spread in the received signal due to attenuation and scattering. We investigate the propagation characteristic of the modulated signal with different communication system parameters. This information can be used to study communication channel reliability.     

Space vector-based analysis of overmodulation in triangle-comparison based PWM for voltage source inverter

The equivalence of triangle-comparison-based pulse width modulation (TCPWM) and space vector based PWM (SVPWM) during linear modulation is well-known. This paper analyses triangle-comparison based PWM techniques (TCPWM) such as sine-triangle PWM (SPWM) and common-mode voltage injection PWM during overmodulation from a space vector point of view. The average voltage vector produced by TCPWM during overmodulation is studied in the stationary (a–b) reference frame. This is compared and contrasted with the average voltage vector corresponding to the well-known standard two-zone algorithm for space vector modulated inverters. It is shown that the two-zone overmodulation algorithm itself can be derived from the variation of average voltage vector with TCPWM. The average voltage vector is further studied in a synchronously revolving (d-q) reference frame. The RMS value of low-order voltage ripple can be estimated, and can be used to compare harmonic distortion due to different PWM methods during overmodulation. The measured values of the total harmonic distortion (THD) in the line currents are presented at various fundamental frequencies. The relative values of measured current THD pertaining to different PWM methods tally with those of analytically evaluated RMS voltage ripple.     

人耳对于不同频率成分分离知觉的定量分析

文章中研究了知觉性声源分离的最基本的问题，即听觉对于不同频率成分特征声源的分离知觉。通过三组听觉辨别实验，定量地分析了不同频率成分特征声源与产生分离知觉的关系，得到了描述这种关系的近似函数，提出了听觉对于不同频率成分特征的分离知觉模型。通过听觉辨别实验得出：两种频率成分的On-set和Off-set的偏离是产生分离知觉的主要原因之一；谐波频率成分之间频率发生的偏移也是产生分离知觉的要因之一；要实现实环境下的知觉性声源分离系统，必须研究各个特征量相互作用时产生的综合结果。     

Vector-optimised harmonic elimination for single-phase pulse-width modulation inverters/converters

A new approach for calculating single-phase inverters/converters-optimised pulse-width modulation (PWM) switching angles for harmonic and voltage control is proposed. This approach takes into account the DC-link voltage ripple, due to the finite DC-link capacitance, in the optimised switching-angles calculation, using its harmonic content. New expressions for the evaluation of the PWM waveform harmonic spectrum are derived. Output voltage quarter-wave symmetry is thus not assumed and the pulse position is no longer fixed, resulting in two simultaneous sets of nonlinear equations in twice as many unknowns as in the case of conventional-optimised PWM strategy with smooth DC input/output voltage. The performance of this latter technique is hence retained while the size of the DC-link capacitor is reduced to a limit depending on the filter capacitance, the number of pulses per half modulation period and the modulation depth. The compensation of the reactive power (exchanged between the AC source/AC load and the DC link due to the rectifying/inverting process and the low-link capacitance) is also included; the converter then plays the additional role of an active power filter. Simulation examples and experimental results are used to validate the proposed method     

矩阵变换器的控制原理及仿真研究

详细介绍了矩阵变换器的拓扑结构及工作原理,并讨论了矩阵变换器的开关函数调制方法和空间矢量调制方法。最后对基于上述两种调制策略的矩阵变换器进行仿真。由结果可知:采用空间矢量调制时电机启动较快,低频和高频时电机的运行性能也好于开关函数调制,但采用开关函数调制时,电机的定子电流谐波特性好于空间矢量调制所得到的结果。     

Measurement of higher harmonics in periodic vibrations using phase-modulated TV holography with digital image processing

We separately measure the higher harmonics vibration patterns of a periodic vibrating object by using time-average TV holography and phase modulation. During measurements the frequency of the phase modulation is adjusted to each harmonic component while the excitation of the object is set low enough to record all components on the linear part of the fringe function. Using acoustical phase stepping and calibration of the fringe function, we compute the amplitude and phase distributions of the frequency component. We measure components up to the 65th harmonic by using square-wave excitation.