频域合成房间频率响应的人工混响方法

给出了一种频域合成房间频率响应的方法用于卷积法人工混响,基于频域内房间频率响应的后期部分为高斯随机过程的假设,用自回归滑动平均模型为其自协方差函数和功率谱密度进行参数化描述,在对自回归滑动平均模型中的参数求解后,通过逆滤波得到了房间频率响应后期部分,与房间频率响应前期部分组合后经过傅里叶反变换得到完整的房间脉冲响应。仿真结果表明该方法的混响效果与镜像源法接近,明显优于反馈延迟网络法,但其计算复杂度比镜像源法低,便于实时应用。     

四阶带通箱的自回归滑动平均模型*

建立扬声器系统的离散时间模型是对其进行数字控制的基础。研究给出了使用LR-2理论优化的四阶带通箱的自回归滑动平均(Autoregressive moving average,ARMA)模型,推导其传递函数方程组,构建其时域差分迭代式,形成离散时间形式的表述,用以描述系统的瞬态行为。实验结果表明,与基于状态空间方程的差分求解方法相比,本文给出的自回归滑动平均模型更为稳定精确,对采样率的要求更低。     

确定性系统一步超前控制算法的探讨

确定性动态系统可以用多种方式进行描述和建模。本文首先探讨了用一种自回归滑动平均模型来描述确定性系统的方法及意义,并在此模型的基础上,引出了适合此种模型的一种最小预测误差控制算法——一步超前控制。并以典型的伺服系统为例,进行了仿真研究及参数、性能分析。     

基于自回归模型的光阱中粒子运动模拟

通过分析光阱中颗粒位移信号特性, 建立描述粒子受限布朗运动过程的自回归模型, 进而提出了一种基于自回归模型的光阱中颗粒运动信号模拟的新方法. 对半径为1 μm的粒子处于光阱刚度分别为10, 20, 50 pN/μm 光阱时的位移信号进行了模拟, 得到的模拟位移信号的自相关函数与理论值相一致. 为了进一步阐明自回归模型的有效性, 在相同光阱参数下, 分别采用自回归模型与蒙特卡罗方法模拟光阱中微粒的位移信号, 采用功率谱法分别对两种模拟方法所得的微粒位移标定光阱刚度, 结果表明自回归模型方法能够取得和蒙特卡洛法相同的精度. 因此, 本文为分析光阱中粒子的随机运动提出了一种新的模拟方法, 可以用来对光阱中的噪声及特性进行分析. 关键词： 光阱 布朗运动 信号模拟 自回归模型     

基于ARMA模型的受损限幅器模型建立方法

针对限幅器遭受功能或物理损伤而发生的非线性效应, 给出了一种基于信号分析的受损限幅器非线性效应研究新视角, 并从该视角出发, 提出了模型建立方法。该方法首先测得受损限幅器幅频响应序列, 将其转化为零均值实平稳序列; 然后计算该序列的自相关函数和偏相关函数, 估计自回归滑动平均(ARMA)模型的阶数; 最后采用最小二乘法估计出模型的表达式, 并采用最终预测误差(FPE)准则对该表达式进行校验。试验结果和理论分析验证了该方法的良好效果。     

基于时变ARMA模型的MEMS陀螺随机误差补偿技术

为了提高微机电系统(MEMS)陀螺的测量精度,提出了一种基于遗忘因子递推最小二乘估计的时变自回归滑动平均(ARMA)模型补偿方法.针对实测MEMS陀螺去除趋势项后的随机漂移信号,采用分段检验方式进行了平稳性分析,选取合适的基函数以及子空间维数进行时变ARMA模型建模.采用遗忘因子递推最小二乘估计的方式进行模型参数估计,通过设置遗忘因子,使得更新后的模型参数能够反映信号的动态变化.针对存在轻微波动的时变参数,采用5阶多项式对时变模型参数进行拟合,并提出一种解析法进行参数寻优,从而建立最优随机漂移模型.将建模结果应用于卡尔曼滤波,进行随机漂移补偿,将补偿结果与时不变ARMA模型建模补偿方式的补偿结果进行对比发现,所提方法补偿后的残差方差比时不变ARMA模型补偿后的残差方差降低了近40%,有效提高了MEMS陀螺随机漂移的补偿精度.     

基于小波分析的ARIMA与LSSVM组合的高炉煤气预测

高炉煤气发生量的准确预测对钢铁企业能源优化调度具有重要意义。针对钢铁企业中基于机理模型的高炉煤气发生量难以准确预测问题,建立了基于小波分析的最小二乘支持向量机(LSSVM)和自回归差分滑动平均(ARIMA)相结合的高炉煤气预测模型。预测前利用小波去噪对原始数据进行消噪处理,并对处理后的数据进行小波变换得到趋势序列和波动序列,然后对各部分序列分别建模和预测,最后将各部分预测结果叠加;仿真结果表明,组合预测模型减小了预测误差,提高了预测精度。与其他模型相比,组合预测模型更适合高炉煤气预测。     

利用对墙截面形状的优化来改善声学小房间的低频响应

提出了通过优化墙截面形状来改变声学小房间低频响应的优化方法。在矩形有限元模型中将墙面用不同的阶梯形状作为墙截面进行代换,并用于具有不同墙面的房间,进行了声场分析。阶梯形状间的差异仅是阶梯高度的取值不同,分别为相等、随机和优化值。将获得优化值的优化方法用于60Hz到120Hz的频率范围内,对不同阶梯墙面以及平墙面房间的频率响应进行了数值计算和比较。结果显示墙截面采用优化值时得到的房间频响最为均匀;将房间长、宽、高比例改变后重复上述数值分析,仍得到房间频响改善在优化情况下最大的结果。对比例较差的房间改善幅度可达4.5dB。另外还以半圆和三角形作为墙截面形状计算了半圆半径和三角形高度分别为固定值和优化值时房间的频率响应,同样得到优化墙面优于固定值墙面的结果。因此通过运用优化的墙截面来改善房间低频声场特性是有意义的。     

基于飞行计划的惯性导航误差模型分析

为了更有效地评估民航飞机惯性导航性能,更好地分析其惯导数据相对于飞行计划的误差。提出一种新方法整体分析惯导误差,将飞行计划航迹离散化计算出误差数据,使用小波多尺度分析方法,经小波变换将误差分为高频与低频两部分,将非平稳的低频部分进行差分处理转化为平稳时间序列,最终建立惯导误差数据的自回归滑动平均（ARMA）模型。通过与实际快速存取记录器（QAR）数据对比验证,此模型能较好地描述惯导误差,较为准确地描述了民航飞机惯性导航误差,为进一步分析其特性及规律奠定了基础。此方法可用于评估民航飞机惯导性能。     

弯曲圆盘换能器与镜像虚源的互辐射作用

建立了弯曲圆盘换能器镜像虚源等效模型,利用脉动球源互作用原理对弯曲圆盘与其镜像虚源的互辐射作用进行理论分析,给出了互辐射阻抗及系统谐振频率的数学表达。提出了虚源互作用的低频换能器设计思想,将刚性反射板引入弯曲圆盘换能器临近辐射面的声场中,通过理论分析、有限元模拟和样机实验研究了低频换能器谐振频率与主要结构参数之间的关系。结果表明,弯曲圆盘与镜像虚源间的互辐射作用可以有效降低换能器的谐振频率,当反射板直径与弯曲圆盘辐射面直径相当时,谐振频率可降低至其自身谐振频率的50%以下;当反射板直径为弯曲圆盘辐射面直径2倍时,谐振频率可降低至37%。      

房间脉冲响应模拟法及混响时间盲估计应用

在构建混响语声数据集时,由于缺乏真实长混响房间脉冲响应且模拟的房间脉冲响应与真实不符,因而导致数据驱动的混响时间盲估计模型性能下降。提出了一种基于条件生成对抗网络的房间脉冲响应模拟法,该方法利用真实的房间脉冲响应训练条件生成对抗网络,可以根据指定的混响时间模拟更加真实的房间脉冲响应。使用不同方法模拟的房间脉冲响应构建训练集用于训练盲估计模型,通过声学实验评估模型性能。实验结果表明,由该方法模拟的房间脉冲响应训练的估计模型在不同信噪比下均具有最小的均方根误差且在长混响情况下显著优于其他模型。     

Improved prewhitening method for linear frequency modulation reverberation using dechirping transformation

This letter presents an autoregressive (AR) prewhitener for linear frequency modulation (LFM) reverberation to enhance the target signal. The proposed method uses a dechirping transformation to inversely compensate the frequency chirp rate of the LFM and give the LFM reverberation a stationary frequency property in each data block. The left or right beam signal adjacent to the current beam is then used as the reference signal, and the frequency response of each data block modeled using the AR coefficients. Finally, these coefficients are used to implement the inverse filter and efficiently prewhiten the LFM reverberation of the current beam.     

基于简正波理论的浅海低频混响时间序列仿真

混响场时域信号序列的数值实现对主动声纳目标模拟器研制具有重要意义。本文所述适用于水平变化浅海环境混响时间序列的一种实现方法,基于现有的浅海简正波相干混响理论。所述方法的思路是通过相干散射场随机序列与发射信号的离散卷积来构成混响时域序列,文中以Pekeris均匀浅海环境为例,给出了相应的混响时间序列仿真结果,并对仿真结果的频谱特性、统计特性、强度衰减以及垂直相关特性等进行了系统检验。结果表明,由仿真混响时间序列所获得的混响特性与理论结果相符,可用于浅海混响序列的仿真。     

Reliability of estimating the room volume from a single room impulse response

The methods investigated for the room volume estimation are based on geometrical acoustics, eigenmode, and diffuse field models and no data other than the room impulse response are available. The measurements include several receiver positions in a total of 12 rooms of vastly different sizes and acoustic characteristics. The limitations in identifying the pivotal specular reflections of the geometrical acoustics model in measured room impulse responses are examined both theoretically and experimentally. The eigenmode method uses the theoretical expression for the Schroeder frequency and the difficulty of accurately estimating this frequency from the varying statistics of the room transfer function is highlighted. Reliable results are only obtained with the diffuse field model and a part of the observed variance in the experimental results is explained by theoretical expressions for the standard deviation of the reverberant sound pressure and the reverberation time. The limitations due to source and receiver directivity are discussed and a simple volume estimation method based on an approximate relationship with the reverberation time is also presented.     

A note on the proper frequency resolution for the room transfer function in the phased beam tracing method

In the simulation of acoustic response of a room, one cannot satisfactorily estimate the transfer function or the impulse response with a sparse frequency resolution. We have studied about the frequency resolution for a satisfactory estimation of room transfer function or the reverberation time using the phased beam tracing method. In order to investigate what happens with the frequency resolution, a number of frequency resolution (0.01-1 Hz), which are usually employed in the numerical analysis, was tested for a room model. It was found that the total accumulated phase in a transfer function and the late part of an impulse response of a room are influenced by the frequency resolution. Main reason for the difference is the correct detection of non-minimum phase zeros, depending on the frequency resolution. A criterion for a proper frequency resolution was suggested by considering the modal density of three-dimensional space. When a sparse dataset was initially given, we showed that cubic spline interpolation can be used to enhance the precision of detection for non-minimum phase zeros.     

Improved space time prewhitener for linear frequency modulation reverberation using fractional Fourier transform

This letter presents an improved space time prewhitening method for linear frequency modulation (LFM) reverberation. The proposed method transforms the reverberation to fractional Fourier domain to whiten using fractional Fourier transform. The linear varying frequency in LFM reverberation is focused on a stationary frequency, and the adjacent block signal is used as the reference signal of prewhitening. Finally, experiment results with real reverberation data verify that the proposed method improves the detection performance of active sonar in shallow sea significantly.     

利用正弦调频信号的宽带速度敏感特性抑制混响

有源声呐探测水中低速目标时,混响与目标回波的频率接近,目标回波与混响分离困难.根据运动目标与产生混响的散射体在速度域的差异,利用正弦调频信号(SFM)的速度敏感特性实现目标回波与混响的有效分离.推导了 SFM信号宽带混响抑制能力与速度分辨模糊之间的约束关系,建立了波形优化设计的搜索模型.通过多普勒滤波处理将数据从频率域...     

Subjective and objective verifications of the inverse functions of binaural room impulse responses

The binaural room impulse responses (BRIRs) can be applied to 3-D sound field reconstruction, virtual reality, noise control, et al. Because the BRIRs are non-minimum phase functions, it is difficult to find the exact inverse functions of the BRIRs, especially when there are two or more sources in a reverberant space. In this work, a method was proposed to find the inverse functions of BRIRs with two sound sources in a reverberant space. The concept of time delays and the method of weighted least squares were used to find the causal, however, approximate inverse functions. The accuracy of the inverse functions was first evaluated objectively by a dummy head system. The result shows that the distortion due to crosstalk and room reverberation can be improved by 16∼18 dB. The inverse functions were also verified subjectively by 20 students. The result of subjective evaluation also shows that the inverse functions can be used successfully to reduce the crosstalk effect and the room reverberation.     

Monotonic curvature of low frequency decay records in reverberation chambers

In the papers by Larsen [1] and Brüel [2], two interesting problems connected with reverberation room measurements are pointed out and discussed. The first problem is that the ensemble averaged decay curve reveals a monotonic curvature at low frequencies. The second phenomenon is that often systematically larger sound power output values are reported at low frequencies according to the free field method than according to the reverberation room method. In searching for an explanation of these anomalies some measurements and a classical normal mode theory analysis have been made. It is shown that it is not possible to explain fully the curvature of the low frequency decay curves by means of the normal mode theory. The measured curves are more bent than the respective theoretical ones. Most probably, it should be possible to explain this lack of agreement by the fact that the absorption characteristics of normal reverberation chambers significantly deviate from the situation of uniform wall admittance which has been assumed in the theoretical deductions. The theoretical analysis and the comparison between theory and practice indicate that the damping characteristics of the individual waves vary much more than is predicted for a uniform wall admittance. This reasoning is supported by the observation that the monotonic curvature increases when a plane concentrated absorbent is added to one of the walls. One way to decrease the curvature has also been identified. When the room surfaces are provided with randomly placed small samples of low frequency absorbents the resulting decay curves turn out to be almost perfectly linear. Furthermore, it is found that the normal mode theory does not imply significantly different sound power output values than the ISO 3741 model. This fact has been verified with a comparative test. According to the normal mode theory the average sound power output as measured in the reverberant room should equal the free field output. Therefore, one is forced to conclude that the analysis of the classical normal mode theory fails in explaining the anomalies observed.     

强吸收-强反射型听音室声场的有限元优化

为获得听音室预期的平直混响时间和合适的房间形状,提出了一种结合强吸收-强反射概念和有限元优化技术的设计方法,并进行了实验验证。对按照优化设计结果所搭建的听音室的房间频率响应、混响时间进行了实际测量,实测数据显示了与解析计算、数值模拟结果有着较好的吻合。在整个设计频段内混响时间特性曲线平直,优化后房间低频段两个倍频程内频率响应的标准偏差可降低约6dB。1/3倍频程中心频率上实测混响时间的方均根值和设计值的偏差在63至4 kHz的6个倍频程内仅为0.02 s。