Spatial Impulse Response Research Articles

Effects of variable acoustic elements on the spatial sound field in multipurpose venues

The design of multipurpose venues typically includes variable acoustic elements which adjust the acoustics of the space to support the intended use. The most common approach to vary the acoustics of a venue is to use variable absorption, often in the form of heavy drapery and/or acoustic felt banners. These elements are often characterized by changes in reverberation time, but their position also impacts the spatial distribution of room energy. In order to study the effects of variable acoustic elements on the three-dimensional sound field at specific audience locations, spatial impulse response measurements were taken in a number of venues using a 32-element spherical microphone array. The venues ranged from a small recital hall of 400 seats to a typical multipurpose hall with 1300 seats to a 2500-seat concert hall with variable acoustics. Beamforming techniques were used to analyze the effects of the variable acoustic elements on the spatial and temporal distribution of sound energy at several receiver locations in each venue. The sound fields in these venues will be compared to those measured in dedicated concert halls, which have been measured for recent work on the topic of listener envelopment. [Work supported by NSF Award 1302741.]

Effective and rapid technique for temporal response modeling of surface acoustic wave interdigital transducers

Surface Acoustic Wave Interdigital Transducers (SAW-IDT) has a considerable application potential for characterization of properties of thin layers, coatings and functional surfaces. For optimization of these SAW-IDTs, it is necessary to study various SAW-IDT configurations by varying the number of electrodes, dimensions of the electrodes, their shapes and spacings. The finite element method (FEM) is generally used to model such transducers but results are obtained in several hours (or days). Thus it is necessary to implement effective and rapid technique for SAW-IDT modeling. In this study, we develop simulation tool based on Spatial Impulse Response model. Therefore, we reduce considerably computing time and results are obtained in a few seconds. In order to validate this method, theoretical and experimental results are compared with finite element method. The results obtained show a good concordance and confirm effectiveness of suggested method. In additional, this method requires less computer memory.

Links between spatial impulse response and binaural dynamic responsiveness in concert halls

Recent research at Aalto University suggests that binaural dynamic responsiveness (BDR) in concert halls is (a) desirable and (b) a result of interaction between the emphasis of higher overtones at stronger dynamic levels and the early response of the room; also that tall, narrow, parallel sided “shoebox” halls have a greater degree of BDR than wider non-shoebox geometries. We have been analyzing the time evolution of spatial impulse responses and their connection to room geometry. In a recent paper, we looked at how wall tilt affects the growth of lateral energy in the room. In this paper, we consider how the shape of forward integrated lateral energy in a spatial impulse response may affect perceived strength, spaciousness, and binaural dynamic responsiveness.

Efficient construction of the spatial room impulse response

An important component of the modeling of sound propagation for virtual reality (VR) is the spatialization of the room impulse response (RIR) for directional listeners. This involves convolution of the listener's head-related transfer function (HRTF) with the RIR to generate a spatial room impulse response (SRIR) which can be used to auralize the sound entering the listener's ear canals. Previous approaches tend to evaluate the HRTF for each sound propagation path, though this is too slow for interactive VR latency requirements. We present a new technique for computation of the SRIR that performs the convolution with the HRTF in the spherical harmonic (SH) domain for RIR partitions of a fixed length. The main contribution is a novel perceptually driven metric that adaptively determines the lowest SH order required for each partition to result in no perceptible error in the SRIR. By using lower SH order for some partitions, our technique saves a significant amount of computation and is almost an order of magnitude faster than the previous approach. We compared the subjective impact of this new method to the previous one and observe a strong scene-dependent preference for our technique. As a result, our method is the first that can compute high-quality spatial sound for the entire impulse response fast enough to meet the audio latency requirements of interactive virtual reality applications.

Modelling and estimation of the spatial impulse response in reverberant conditions

Modern audio signal processing and speech enhancement relies more and more on machine learning approaches, which require vast amount of data for training. One of the ways to create a dataset for training is by convolving measured impulse response between the sound source and the device with clean speech and adding noise. This approach is limited to the pair of used sound source and microphone, as it incorporates not only the reverberation of the room, but also the radiation pattern of the sound source (typically mouth simulator or head and torso simulator) and the directivity patterns of the microphones in the device under test. In this paper we propose using a spherical loudspeaker array as a transmitter and a spherical microphone array as a receiver to create a sound source and receiver independent impulse response. During the dataset synthesis this spatial impulse response is modified to model the impulse response between transmitter and receiver with given directivity patterns.

Room measurement setup for accurate objective analysis and realistic subjective comparison of concert halls

When measuring a concert hall, a primary goal is to characterize the perceptual aspects of the room’s quality. Since subjective testing requires extensive time and resources, halls are often compared using objective metrics designed to correlate with perception. The goal of the present work is to create a concert hall measurement database that allows for both accurate objective and realistic subjective assessment of concert halls. A 32-element spherical microphone array is used to capture a spatial room impulse response (SRIR) within a hall. A three-way omnidirectional sound source is used for objective measurements, exhibiting omnidirectional behavior up to 5kHz. The omnidirectional SRIR can be used to calculate typical room acoustic metrics and analyzed using beamforming techniques. For a realistic auralization that resembles an orchestral performance, an alternate sound source was used: a compact 20-element spherical loudspeaker. This loudspeaker can be moved around a stage and the measurement signal c...

Investigating energy integration time limits for listener envelopment perception using a real-time adaptable hybrid impulse response method

Listener envelopment (LEV), the sense of being immersed in a sound field, is a common perception in concert hall acoustics, but more work is needed to establish a metric. The objective of this research is to further investigate LEV utilizing custom software building on Dick & Vigeant’s previous research to understand what contributes most to LEV in a concert hall (JASA 140:3175 2016). For this study, spatial room impulse response (SRIR) measurements were obtained using a 32-channel spherical microphone array in different performance venues. These SRIRs were used in a subjective listening test and processed for 3rd order Ambisonic reproduction over a 30-loudspeaker array. Utilizing a custom testing interface developed in Max 7, pairs of equal-length SRIRs with contrasting high and low LEV were time-windowed and summed together to create a hybrid SRIR. A dial in the interface controlled the hybrid SRIR’s time transition point, and subjects were asked to adjust the timing dial to the point at which they perceived the highest sense of LEV. Results will be presented showing the integration limits that produced noticeable changes in LEV and implications to the proposed LEV metric will be discussed. [Work was supported by NSF Award 1302741.]

Spatial analysis and auralization of room acoustics using a tetrahedral microphone

A compact tetrahedral microphone array is used to measure several controlled sound fields and compare the analysis of spatial room impulse responses with two methods: spatial decomposition method (SDM) and IRIS, a commercial system based on sound intensity vector analysis. Results suggest that the spatial accuracy of both methods is similar and in most cases the error is comparable to the localization uncertainty of human listeners. Furthermore, a listening test is conducted comparing three 3D-sound fields and their SDM auralizations. Results suggest that the similarity of the auralized and original sound fields depends on the target room and stimulus.

Fixed-effects dynamic spatial panel data models and impulse response analysis

Real data often have complicated correlations over cross section and time. Such correlations are of particular interests in empirical studies. This paper considers using high order spatial lags and high order time lags to model complicated correlations over cross section and time. We propose to use the quasi maximum likelihood (QML) method to estimate the model. We establish the asymptotic theory of the quasi maximum likelihood estimator (QMLE), including the consistency and limiting distribution, under large N and large T setup, where N denotes the number of individuals and T the number of time periods. We investigate the problem of estimating impulse response functions and the associated (1−α)-confidence intervals. Average direct, indirect and total impacts are defined along the same spirits of LeSage and Pace (2009) under the dynamic spatial panel data setup. The estimation and inferential theory for the three impacts are studied. Model selection issue is also considered. Monte Carlo simulations confirm our theoretical results and show that the QMLE after bias correction has good finite sample performance.

A Fast Method to Calculate the Spatial Impulse Response for 1-D Linear Ultrasonic Phased Array Transducers.

A method is developed to accurately determine the spatial impulse response at the specifically discretized observation points in the radiated field of 1-D linear ultrasonic phased array transducers with great efficiency. In contrast, the previously adopted solutions only optimize the calculation procedure for a single rectangular transducer and required approximation considerations or nonlinear calculation. In this research, an algorithm that follows an alternative approach to expedite the calculation of the spatial impulse response of a rectangular linear array is presented. The key assumption for this algorithm is that the transducer apertures are identical and linearly distributed on an infinite rigid plane baffled with the same pitch. Two points in the observation field, which have the same position relative to two transducer apertures, share the same spatial impulse response that contributed from corresponding transducer, respectively. The observation field is discretized specifically to meet the relationship of equality. The analytical expressions of the proposed algorithm, based on the specific selection of the observation points, are derived to remove redundant calculations. In order to measure the proposed methodology, the simulation results obtained from the proposed method and the classical summation method are compared. The outcomes demonstrate that the proposed strategy can speed up the calculation procedure since it accelerates the speed-up ratio which relies upon the number of discrete points and the number of the array transducers. This development will be valuable in the development of advanced and faster linear ultrasonic phased array systems.

A periodic spatio-spectral filter for event-related potentials

With respect to single trial detection of event-related potentials (ERPs), spatial and spectral filters are two of the most commonly used pre-processing techniques for signal enhancement. Spatial filters reduce the dimensionality of the data while suppressing the noise contribution and spectral filters attenuate frequency components that most likely belong to noise subspace. However, the frequency spectrum of ERPs overlap with that of the ongoing electroencephalogram (EEG) and different types of artifacts. Therefore, proper selection of the spectral filter cutoffs is not a trivial task. In this research work, we developed a supervised method to estimate the spatial and finite impulse response (FIR) spectral filters, simultaneously. We evaluated the performance of the method on offline single trial classification of ERPs in datasets recorded during an oddball paradigm. The proposed spatio-spectral filter improved the overall single-trial classification performance by almost 9% on average compared with the case that no spatial filters were used. We also analyzed the effects of different spectral filter lengths and the number of retained channels after spatial filtering.

The analysis of optical wave beams propagation in lens systems

In this paper some aspects of the formation and propagation of optical wave beams in lens systems were considered. As an example, the two-lens optical information processing system was considered. Analysis of the two-lens optical circuit has been made with a systems approach perspective. As part of the radio-optical analogies had been applied certain provisions of the theory of dynamical systems to the spatial optical system. The lens system is represented as a simple series-connected optical elements with known spatial impulse response. General impulse response of such a system has been received, as well as consider some special cases of the impulse response. The question of the relationship between the parameters and the size of the input aperture lenses for undistorted transmission of the optical signal has been considered. Analysis of the energy loss resulting from the finite aperture of the lens. It's based on an assessment of the fraction of radiation that propagates beyond the lens. Analysis showed that the energy losses depend explicitly on the following parameters: radiation wavelength, distance between input aperture and lens, and ratio of the input aperture and lens aperture. With the computer help simulation the dependence of losses was shown on the above parameters

Hybrid Seminumerical Simulation Scheme to Predict Transducer Outputs of Acoustic Microscopes

We present a seminumerical simulation method called SIRFEM, which enables the efficient prediction of high-frequency transducer outputs. In particular, this is important for acoustic microscopy where the specimen under investigation is immersed in a coupling fluid. Conventional finite-element (FE) simulations for such applications would consume too much computational power due to the required spatial and temporal discretization, especially for the coupling fluid between ultrasonic transducer and specimen. However, FE simulations are in most cases essential to consider the mode conversion at and inside the solid specimen as well as the wave propagation in its interior. SIRFEM reduces the computational effort of pure FE simulations by treating only the solid specimen and a small part of the fluid layer with FE. The propagation in the coupling fluid from transducer to specimen and back is processed by the so-called spatial impulse response (SIR). Through this hybrid approach, the number of elements as well as the number of time steps for the FE simulation can be reduced significantly, as it is presented for an axis-symmetric setup. Three B-mode images of a plane 2-D setup-computed at a transducer center frequency of 20MHz-show that SIRFEM is, furthermore, able to predict reflections at inner structures as well as multiple reflections between those structures and the specimen's surface. For the purpose of a pure 2-D setup, the SIR of a curved-line transducer is derived and compared to the response function of a cylindrically focused aperture of negligible extend in the third spatial dimension.

Direction of Arrival Estimation of Reflections from Room Impulse Responses Using a Spherical Microphone Array

This paper studies the direction of arrival estimation of reflections in short time windows of room impulse responses measured with a spherical microphone array. Spectral-based methods, such as multiple signal classification (MUSIC) and beamforming, are commonly used in the analysis of spatial room impulse responses. However, the room acoustic reflections are highly correlated or even coherent in a single analysis window and this imposes limitations on the use of spectral-based methods. Here, we apply maximum likelihood (ML) methods, which are suitable for direction of arrival estimation of coherent reflections. These methods have been earlier developed in the linear space domain and here we present the ML methods in the context of spherical microphone array processing and room impulse responses. Experiments are conducted with simulated and real data using the em32 Eigenmike. The results show that direction estimation with ML methods is more robust against noise and less biased than MUSIC or beamforming.

Parametric study of an ultrasonic non-destructive testing problem based on the reciprocity principle and a hybrid numerical method

Numerical simulations are needed for both the design and the improvement of Ultrasound Non-Destructive Testing techniques in industry. One typical configuration is the pulse echo immersion testing of a material with a possible crack. This is a large and multiscale elastodynamic problem, for which the computation may be intensive using standard discrete methods. Different approaches have been proposed to gain efficiency in terms of the computation time, as i) the hybridization of a discrete method with a semi-analytical formulation or ii) using the reciprocity principle to separate the calculation of the field radiated by the crack from the field in the same material. We present a numerical strategy based on those two approaches in order to perform 3D simulations with a possible parametrization of the crack geometry and location. First, the Spatial Impulse Response (SIR) of a focalized transducer in water is computed using a semi-analytical software. Then, we show that the calculation of the SIR can be pursued in the same elastic material using a FDTD method. To take into account the effects of the crack, this SIR is used in conjunction with the time domain reciprocity equation. This process allows performing an efficient computation of the echo signal from the crack. Results and comparisons with experimental measurements will be presented in a 2D case.

Spatial Impulse Response Assessment in Room Acoustics Auralization

Spatial Impulse Response Assessment in Room Acoustics Auralization

Evaluation of the spatial impulse response of planar ultrasonic radiators

A method for evaluating the spatial impulse response for a planar source having arbitrary velocity and delay distribution is presented. The time-domain approach is based on the Rayleigh integral formulation for the velocity potential. To obtain the velocity potential one must evaluate and superpose the contribution from each elemental element of the radiator. This step entails the accumulation of the amplitude contribution from each elemental source arriving at the observation point at a prescribed time. The problem of sorting of these arrivals is examined in this work and procedures for mapping the algorithm for implementation on general-purpose graphics processing units are presented.

An open-source spherical microphone array design

We present an open-source design for producing a spherically baffled, 32-channel microphone array having elements aligned with the vertices and face centers of a dodecahedron, and fabricated using additive manufacturing (3-D printing). The design approach emphasized low cost, assembly ease, and acoustic integrity. Mechanical, electrical, and acoustical design considerations are discussed, as are assembly and calibration details. The baffle is a 10-cm-radius sphere, built from separable hemispheres, and supported by a 2-cm-diameter cylindrical stand that serves as a conduit for the microphone signal cables. Microphone capsules are mounted on preamp boards, which provide balanced line level outputs, and press fit to the baffle. The performance of the array is characterized, and an example application to spatial room impulse response measurement is provided. Design documents, including the enclosure model and preamp electrical design and board layout, are provided at https://ccrma.stanford.edu/~granzow/sphericalmicarray/

Photoacoustic imaging of nanoparticle- containing cells using single-element focused transducer: a simulation study.

A new theoretical approach for photoacoustic (PA) image simulation of an ensemble of cells with endocytosed gold nanoparticles is presented. Each cell was approximated as a fluid sphere and suspended in a nonabsorbing fluid medium. It was assumed that the cellular optical absorption coefficient changed greatly because of endocytosis of nanoparticles; however, thermophysical parameters remained unchanged because nanoparticles occupied negligible intracellular volume. A frequency-domain method was used to obtain a PA signal from a single cell and resultant signal detected by a focused single-element transducer was evaluated by convolving signals from many cells with the spatial impulse response function of the receiver. The proposed model was explored to simulate PA images of numerical phantoms. It was observed that features of the phantoms are retained precisely in those simulated images. Also, speckles in PA images are significantly suppressed because of strong boundary buildup when cells are bounded to a region. Nevertheless, speckle visibility increases when cells are not bounded to a region. This approach may be developed as a realistic simulation tool for PA imaging of tissue medium utilizing its cellular feature.

Modelling based on Spatial Impulse Response Model for Optimization of Inter Digital Transducers (SAW Sensors) for Non Destructive Testing

This study deals with modelling SAW-IDT transducers for their optimization. These sensors are specifically developed to characterize properties of thin layers, coatings and functional surfaces. Among the methods of characterization, the ultrasonic methods using Rayleigh surface waves are particularly interesting because the propagation of these waves is close to the surface of material and the energy is concentrated within a layer under the surface of about one wavelength thick. In order to characterize these coatings and structures, it is necessary to work in high frequencies, this is why in this study, SAW-IDT sensors are realized for surface acoustic wave generation. For optimization of these SAW-IDT sensors, particularly their band-width, it is necessary to study various IDT configurations by varying the number of electrodes, dimensions of the electrodes, their shapes and spacings. Thus it is necessary to implement effective and rapid technique for modelling. The originality of this study is to develop simulation tools based on Spatial Impulse Response model. Therefore it will be possible to reduce considerably computing time and results are obtained in a few seconds, instead of several hours (or days) by using finite element method. In order to validate this method, theoretical and experimental results are compared with finite element method and Interferometric measurements. The results obtained show a good overall concordance and confirm effectiveness of suggested method.