多声道录音方法(四)

九、人工延时与人工混响的使用使用人工延时与人工混响模拟厅堂音响效果的制作原理与方法,可详见《录音音响学》,这里主要谈以人工延时与人工混响制作"电声音响"效果的原理与方法,这是多声道录声中经常制作的一种音响效果.所谓"电声音响",即是以人工延时与人工混响制作出来的一种非厅堂的混响感与空间感.我们知道,混响与延时本为室内声学的概念,是与厅堂及反射声场的概念联系在一起的."电声音响"虽然也是由反射声场的音响概念脱胎而来,但已经打破了模拟厅堂等反射声场的音响概念.已不再遵循模拟厅堂的延时与混响所要求的程序与限值.所以,给人们的音响印象也就不是厅堂的自然延时与混响,而纯粹是一种"电声音响"效果了.     

音乐厅中的声扩散设计初探

声扩散设计对厅堂音质的影响缺乏定量描述.以海南大学音乐厅的声学设计为例,运用快速多极子边界元法(FMBEM)对声扩散的影响进行定量分析,在侧墙使用一维伪随机序列结合视觉艺术效果优化其散射性能,在后墙直接采用二维伪随机序列生成立体的扩散结构,解决了音乐厅平面选型带来的声学缺陷问题.数值模拟及现场测量显示,在采用扇形与矩形结合平面的小音乐厅中,声扩散设计比平面更有优势,使该音乐厅的中前场及中间位置获得足够的侧向反射声能,使厅堂各区域的音质参量取值落在推荐的范围之内.     

厅堂中的立体声扩声技术

文中叙述了应用于音乐演奏或者艺术表演大厅中的立体声技术:其中包括立体声扩声、立体混响和厅堂中初始反射声音的模拟三个方面。讨论了这三个系统的原理及其使用条件,并且指出:这些系统只有被正确使用时,它才可以用以改善或者控制厅堂的声学特性。     

厅堂音质的可听化计算机模拟

厅堂音质的可听化计算机模拟是目前厅堂音质和电声设计中的新技术，通过计算机模拟厅堂中的听音环境，从而厅堂的设计阶段就进行音质效果的评价。本文对厅堂音质的可听化模拟技术的基本原理和过程作了简单的介绍，同时针对目前厅堂音质的计算机模拟算法在模拟复杂声场时的局限民生作了分析。     

室内声学设计中早期反射声的作用及控制

简述了哈斯效应和梳状滤波效应及其对主观听音的影响,然后对厅堂和听音室早期反射声的作用及控制进行说明,重点说明了厅堂最佳侧向反射声和听音室或控制室最佳初始延时,最后介绍了反射面有效工作频率下限的计算公式.     

厅堂音质设计的要求

厅堂音质的评价量比较多,但物理评价量与主观听感之间尚未完满地对应。在现阶段,要做好厅堂音质设计,关键是把握好合适的混响时间,具有较多的早期侧向反射声以及消除不利反射声和降低噪声。     

厅堂中反射声能累积值（REC）的测试研究

本文通过对厅堂中反射声能累积值的实测，讨论了其在厅堂中的分布特性，同时与稳态声场中声压级的分布相比较，指出ＲＥＣ作为厅堂中响度评价的参量，比稳态声压级更加合理。     

厅堂音质设计第一讲 观众厅音质设计的工程方法

电声学和建筑声学是声学的二个专业分支,在近代观众厅的扩声系统设计中,这两项专业分支就融为一体了,从系统的观点看,观众厅建筑音质设计应作为扩声系统的一个组成部分,因此作为从事扩声系统设计的电声工程师来说,需要了解观众厅建筑音质设计的专业技术知识。本讲座除了介绍该方面的专业知识外,还引用了大量的国内外厅堂设计实例及实测数据,因此对于厅堂音质设计的同志颇有教益。本讲座分两大部分用四讲刊出,第一部分叙述响度、混响时间、前次(早期)反射声、扩散等观众厅性能参数的设计关系(分三讲);第二部分叙述观众厅体积、尺寸比例、体型、吸声处理等建筑设计参数的常规考虑的设计步骤(第四讲)。至于电声系统设计、扬声器和传声器选择、布置将另有文章介绍。     

RASTI预测值与STI模拟值的比较

用ODEON软件模拟了4个厅堂的声场,得到了每个厅堂内3个受声点的语言传输指数STI的模拟值;同时通过Peutz公式预测了这些受声点的快速语言传输指数RASTI预测值。比较模拟值与预测值发现：模拟值和预测值的线性相关系数较高,但两者并不一致。     

厅堂声场的电声控制技术

厅堂音质设计是建筑声学设计的一个重要内容。近年来,在厅堂音质设计中有两个引人注目的发展动向,一是利用计算机的室内声场模拟,在建筑声学上实现音质设计的动向;二是利用引入电声设备支援和控制声环境,即所谓声场控制的动向。本文着重叙述有关声场控制技术,并阐述它的原理和各种运用方法。厅堂的声场控制之所以日益引起人们的注目和应用,其背景主要是由于多功能厅堂的日     

Variable delay for acoustic surface waves by electro-acousto-optic interaction

Continuosly variable analogue delay is demonstrated by using reflections from a laser-light-induced impedence discontinuity on a photoconductive layer evaporated on an LiNbO3 delay line at 75 MHz. ?30dB reflection loss is obtained with a delay range of 20 ?s.     

动目标多径回波的时延、到达角和多普勒频率联合估计

动目标回波的时延、到达角与多普勒频率等参数,都是定位与跟踪目标所需的重要参数。本文针对动目标多径回波的参数估计问题,利用照射信号的周期重复性建立了具有旋转不变结构的阵列接收信号模型,并将PRO-ESPRIT算法应用于该信号模型,从而利用模型中的旋转不变因子及其对应的特征向量估计得到各多普勒频率、时延和到达角参数。这一方法对阵列形式没有特殊要求;与已有的联合估计方法相比,多参数联合估计时无需高维搜索或迭代,估得的对应相同回波的信号参数自动配对;在照射信号未知及存在相同多普勒频率参数的条件下,仍具适用性。计算机仿真结果证实了该方法的有效性。     

Group delay ripple resulting from multiple reflections in SAW devices

A simple formula is derived for the spurious fractional group delay ripple in the passband of systems with delay. This same formula also gives the spurious amplitude ripple in the passband. These spurious ripples are due to multiple reflections in the system, and it is shown that the fractional peak-to-peak ripple is a function of only the round-trip reflection loss or triple-transit ratio.     

A ray-tracing propagation model for digital broadcast systems inurban areas

A propagation model is presented for characterizing the channel response for digital systems in urban areas where multiple reflections from buildings are encountered. A deterministic ray-tracing propagation model is used to predict the time delay and fading characteristics for the channel in a hypothetical urban area. The analysis shows that due to multiple reflection and diffraction sources, the RMS delay spread of the channel in urban areas can be several hundred nanoseconds, so that very effective equalizers will be required to achieve successful performance of high-data-rate digital systems such as 20-Mb 16-QAM digital HDTV. The channel response results presented also suggest that polarization diversity may be a useful technique for mitigating some of the channel impairments predicted by the propagation model     

低频多跳天波时延估计算法比较

低频天波传播时延的准确预测对其在远程导航授时中的应用潜力挖掘具有重要意义. 为了获得地-电离层波导中低频多跳天波模式的传播时延特性,同时验证典型多径时延估计算法在不同信道环境下的作用性能,文中首先采用时域有限差分(finite-difference time-domain, FDTD)电磁计算方法对不同电离层反射情况下的距发射台400 km处地面接收的低频天地波耦合总场进行正演预测,然后分别基于快速傅里叶变换(fast Fourier transform, FFT)/快速傅里叶逆变换(inverse fast Fourier transform, IFFT)频谱相除、多重信号分类(multiple signal classification, MUSIC)和旋转不变技术信号参数估计(estimating signal parameters via rotational invariance techniques, ESPRIT)三种算法对电磁场数值预测结果进行后处理,解耦得到不同模式（地波、一跳天波、二跳天波、三跳天波及四跳天波）的时延,并在此基础上分析比较了无噪声和信噪比(signal-noise ratio, SNR)为0 dB、?5 dB以及?10 dB情况下三种算法对多跳天波的时延估计结果. 结果表明,波跳次数越高,算法的检测能力越差. 对于文中所模拟的信道条件,在弱噪声（SNR=0 dB）、电离层强反射时,FFT/IFFT算法结果精度最高,时延误差不超过400 ns;而在强噪声（SNR= ?10 dB）、电离层弱反射时,ESPRIT算法稳定性最好,误差范围在5 μs以内.     

Design of Group Delay Time Controller Based on a Reflective Parallel Resonator

In this paper, a group delay time controller (GDTC) is proposed based on a reflection topology employing a parallel resonator as the reflection termination. The design equations of the proposed GDTC have been derived and validated by simulation and experimental results. The group delay time can be varied by varying the capacitance and inductance at an operating frequency. To show the validity of the proposed circuit, an experiment was performed for a wideband code division multiple access downlink band operating at 2.11 GHz to 2.17 GHz. According to the experiment, a group delay time variation of 3±0.17 ns over bandwidth of 60 MHz with excellent flatness is obtained.     

An algorithm for successive identification of reflections

A new algorithm for successive identification of seismic reflections is proposed. Generally, the algorithm can be viewed as a curve matching method for images with specific structure. However, in the paper, the algorithm works on seismic signals assembled to constitute an image in which the investigated reflections produce curves. In numerical examples, the authors work on signals assembled in CMP gathers. The key idea of the algorithm is to estimate the reflection curve parameters and the reflection coefficients along these curves by combining the multipulse technique and the generalized Radon transform. The multipulse technique is used for wavelet identification in each trace, and the generalized Radon transform is used to coordinate the wavelet identification between the individual traces. Furthermore, a stop criterion and a reflection validation procedure are presented. The stop criterion stops the reflection estimation when the actual estimated reflection is insignificant. The reflection validation procedure ensures that the estimated reflections follow the shape of the investigated reflection curves. The algorithm is successfully used in two numerical examples. One is based on a synthetic CMP gather, whereas the other is based on a real recorded CMP gather. Initially, the algorithm requires an estimate of the wavelet that can be performed by any wavelet estimation method.     

Reflection of pulses in a nonlinear random medium with strong fluctuations

The reflection of delta pulses from a strongly fluctuating nonlinear random medium is studied. With the use of the equation of a backscattered field obtained by the invariant imbedding method, a numerical algorithm is developed for solving the one-dimensional direct and inverse problems of wave reflection in time representation. The solutions obtained can be used for investigation of the fluctuation-related features of reflections occurring in nonlinear random media and in the design of remote sensing methods. The conditions that give rise to wave stochastic resonance and dynamic effects in nonlinear random reflections are considered.     

The transient response of a dipole antenna using a summationapproach in technique (SAT)

A novel summation approach in technique (SAT) improving on the usual computation by multiple reflections to find the transient response was presented in a previous paper. This technique leads to accurate answers consisting of relatively few terms. The transient response at large values of time can be found without need to know explicitly and laboriously add all multiple reflections for the whole preceding range of time involved in producing the response. In this paper, the transient response for a realistically modeled pulse generator exciting a dipole antenna modeled as a distributed parameter load is investigated using a generalization of the SAT. A detailed comparison between this technique and the standard superposition of multiple reflections is presented     

A new driver circuit for chip-to-chip signal transmission in Josephson packaging

A new driver circuit is developed for chip-to-chip logic signal transmission in Josephson computers. Multiple reflection noises between driver and connector impedance discontinuities may cause false logic operations in the driver and receiver circuits. Based on this factor, the driver is designed to match the impedance between the driver and transmission line in order to reduce multiple reflections. Since the noises due to the first reflections remain in this driver system, its use is limited to special cases. When used in these cases, however, the driver provides a shorter transmission path delay than Klein's driver. Experimentation shows that the driver has perfect impedance matching effects within a wide bias current margin (±26 percent).