Generating Artificial Reverberation via Genetic Algorithms for Real-Time Applications

We introduce a Virtual Studio Technology (VST) 2 audio effect plugin that performs convolution reverb using synthetic Room Impulse Responses (RIRs) generated via a Genetic Algorithm (GA). The parameters of the plugin include some of those defined under the ISO 3382-1 standard (e.g., reverberation time, early decay time, and clarity), which are used to determine the fitness values of potential RIRs so that the user has some control over the shape of the resulting RIRs. In the GA, these RIRs are initially generated via a custom Gaussian noise method, and then evolve via truncation selection, random weighted average crossover, and mutation via Gaussian multiplication in order to produce RIRs that resemble real-world, recorded ones. Binaural Room Impulse Responses (BRIRs) can also be generated by assigning two different RIRs to the left and right stereo channels. With the proposed audio effect, new RIRs that represent virtual rooms, some of which may even be impossible to replicate in the physical world, can be generated and stored. Objective evaluation of the GA shows that contradictory combinations of parameter values will produce RIRs with low fitness. Additionally, through subjective evaluation, it was determined that RIRs generated by the GA were still perceptually distinguishable from similar real-world RIRs, but the perceptual differences were reduced when longer execution times were used for generating the RIRs or the unprocessed audio signals were comprised of only speech.     

基于变换声学的角反射器的设计*

基于超材料的新型声学器件是近年来的研究热点,变换声学为这些新型声学器件的实现带来了可能。该文提出了一种基于变换声学的声反射器模型的设计方法。通过简单的线性映射,该声反射器具有均匀而各向异性的参数。利用Biot流体等效介质理论,通过周期分层结构可以对该反射器进行实现。仿真结果显示,在一定角度范围内,该反射器可以将声波按照入射方向进行反射,同时也验证了该结构的宽频有效性。     

澜沧江某电站左岸地下洞室群围岩稳定性的FLAC~(3D)分析

在岩体结构模型概化的基础上,采用FLAC3D数值分析方法,系统研究了澜沧江某大型水电站大跨度、高边墙地下洞室群开挖完成后围岩的二次应力场、变形场和塑性破坏区的变化特征。总结了地下洞室群围岩应力、变形和破坏区的分布特征和变化规律,为洞室群稳定性评价和工程施工设计提供了基础资料和参考依据。     

琅玡山抽水蓄能电站厂房位置及轴线方向的优化选择

地下厂房位置及轴线方向的选择是一项重要的地质工作,本文在分析琅山抽水蓄能电站厂房区工程地质条件的基础上,就厂房位置及其轴线方向的优化选择,进行了分析和研究。     

波涡相互作用研究的某些进展(Ⅱ)

<正> 5 波涡共振 从第3节的感受性问题再前进一步,自然要问在什么条件下入射波激发起涡中之波的最大响应.这就导致了入射波与层状或轴状涡中受激波之间共振的概念,简称波涡共振.一般说来,在流体内部若有两个或多个波相会,它们将互相穿透而沿原来的方向离去.但若它们的波矢量和频率满足一定的关系(参见Craik 1985),就会在相会点产生新的波.2阶扰动的振幅可达到1阶扰动振幅的量级,而且流场中会出现一些重要的独特性质.这就是流体内部波共振,波涡共振是其一类情形.     

大规模声学边界元法的GPU并行计算

提出一种大规模声学边界元法的高效率、高精度GPU并行计算方法.基于Burton-Miller边界积分方程,推导适于GPU的并行计算格式并实现了传统边界元法的GPU加速算法.为提高原型算法的效率,研究GPU数据缓存优化方法.由于GPU的双精度浮点运算能力较低,为了降低数值误差,研究基于单精度浮点运算实现的double-single精度算法.数值算例表明,改进的算法实现了最高89.8％的GPU使用效率,且数值精度与直接使用双精度数相当,而计算时间仅为其1/28,显存消耗也仅为其一半.该方法可在普通PC机(8GB内存,NVIDIA GeForce 660 Ti显卡)上快速完成自由度超过300万的大规模声学边界元分析,计算速度和内存消耗均优于快速边界元法.     

Effects of sound on flow separation from blunt flat plates

The effect of sound on the flow around plates with semicircular or square leading edges and square trailing edges located in a low turbulence open jet has been studied. In all circumstances the length of the leading edge separation bubbles associated with square leading edge plates was found to oscillate. When sound was applied to the flow around these plates, the leading edge shear layers reattached closer to the leading edge and the oscillations in bubble length occurred at the applied sound frequency, generating patches of concentrated vorticity in the boundary layers. These vorticity patches moved downstream near the plate surface and then beyond the trailing edge to form vortex cores in a street with a Strouhal number equal to the applied sound value. Sometimes these vortex streets are unstable and break down into streets with Strouhal numbers approaching those observed without sound. These effects of sound were not observed in the flow around plates with semicircular leading edges. Without sound, square leading edge plates of intermediate length did not shed regular vortex streets.     

Mass,momentum and total excess energy transported by a weak planeN wave

A weakly nonlinear plane acoustic wave is emitted into an ideal gas of semi-infinite extent from an infinite plate by its sinusoidal motion of single period. The wave develops into anN wave in the far field, as long as the energy dissipation is negligible everywhere except for discontinuous shock fronts. The third-order effects at shock fronts are evaluated, i.e., the generation of reflected acoustic wave as a result of the interaction of shock and expansion wave and the production of entropy by the energy dissipation at shock fronts. Consideration of these effects enables one to estimate the whole mass, momentum and total excess energy (sum of the kinetic energy and excess of internal energy over an initial undisturbed value) transported by theN wave to the accuracy of third order of wave amplitude. It is shown that the mass and total excess energy transported by theN wave increase and the momentum decreases to asymptotic limits as the wave propagates. The result shows good agreement with a numerical result obtained by solving the Euler equations with a high-resolution TVD upwind scheme.     

Self-switching of displacement waves in elastic nonlinearly deformed materialsSelf-commutation d'ondes de déplacement dans les milieux élastiques non-linéaires

The problem of self-switching plane waves in elastic nonlinearly deformed materials is formulated. Reduced and evolution equations, which describe the interaction of two waves the power pumping wave and the faint signal wave are obtained. For the case of wave numbers matching the pumping and signal waves, a procedure of finding the exact solution of evolution equations is described. The solution is expressed by elliptic Jacobi functions. The existence of the power wave self-switching is shown and commented. To cite this article: J. Rushchitsky, C. R. Mecanique 330 (2002) 175–180.