Simulated Impulse Responses Research Articles

Quantifying a measure and exploring the effect of varying reflection densities from realistic room impulse responses

Perceptual studies using objective acoustic metrics calculated from room impulse responses, such as reverberation time and clarity index, are common. Less work has been conducted looking explicitly at the reflection density, or the number of reflections per second. The reflection density, though, may well have its own perceptual influence when reverberation time and source-receiver distances are controlled, particularly in relation to room size perception. This paper presents first an investigation into quantifying the reflection density from realistic room impulse responses that may be measured or simulated. The resolution of the sampling frequency, time window applied, and cut-off level for including a reflection in the count are considered. The quantification method is subsequently applied to select a range of realistic RIRs for use in a perceptual study on determining the maximum audible reflection density by humans, using both speech and clapping signals. Results from this study are compared to those from similar previous work by the authors which used artificially simulated impulse responses with constant reflection densities over time.

Comparison of Strategies to Model Spatial Fluctuations of Room Acoustic Single Number Quantities

In a number of independent empiric studies it was shown that room acoustic single number parameters vary severely with small changes of the source and microphone position. Presently there is no evidence that these spatial fluctuations can be modelled using simulated impulse responses. As a result there is limited knowledge about the origin and the contributing influence factors of this variance over space. In this contribution the results of simulations using wave based as well as ray tracing simulations are compared to each other. It will be discussed if these simulations are able to predict the fluctuations that were found in measurement series taken in a number of different auditoria.

다수의 스피커를 사용하는 선형 배열 시스템에서 기하학적 접근 방법을 통한 스윗 스팟 분석

This paper describes techniques used to analyze the sweet spot of sound field reproduced by ear-level linear arrays of loudspeakers by geometrical approach method. Previous researches have introduced various sweet spot definitions in their own way. In general, sweet spot is defined as an area whose stereophonic sound effect is valid. Its size is affected by the geometrical arrangement of the system. In this paper, a case when plane waves are generated by linear arrays of loudspeakers in the horizontal plane is considered. So the sweet spot is defined as an area in which the listener can perceive the desired azimuth angle. Because there are many loudspeakers, impulse responses at listener's ears are in the form of pulse-train and the time-duration of the pulse-train affects the localization performance of the listener. So we calculated the maximum time duration of pulse-train by geometrical approach method and identified with the results of impulse response simulation. This paper also includes parameter analysis with respect to aperture size, so it suggests a tool for sound engineers to expect the sweet spot size and listener's sound perception.

Estimation of angle-dependent mode coupling and attenuation in step-index plastic optical fibers from impulse responses

We report on a method for estimation of angle-dependent mode coupling and attenuation in step-index plastic optical fibers (SI-POFs) from the shapes of impulse responses at two different fiber lengths. While alternating the fiber lengths, deviations between simulated and reference impulse responses are minimized by optimizing both mode coupling and attenuation parameters using pattern-search routines. Applying a matrix-based finite-difference approach to Gloge's time-dependent power flow equation fast computation of simulated impulse responses is enabled. We demonstrate that mode-dependent coupling and attenuation parameters converge to values that reconstruct fiber characteristics reported by other authors. We show that our results can be used for prediction of impulse responses, yielding determination of frequency responses, fiber bandwidths and coupling lengths. We conclude that our method enables characterization of SI-POFs from fiber impulse response measurements.

Using the Kurtosis Measure to Identify Clusters in Wireless Channel Impulse Responses

In wireless channel propagation, multipath arrivals appear at the receiver in clusters. Because the notion of clusters tends to be intuitive rather than well-defined, cluster identification in channel impulse responses has traditionally been carried out through human visual inspection. Besides time-consuming for large-scale measurement campaigns, this approach is subjective and will vary from person to person, leading to arbitrary identification. In response to these concerns, automatic clustering algorithms have emerged in the past decade. Most, however, are laden with settings which are sensitive to different radio-frequency environments, again subject to arbitrariness. In this communication we propose a novel clustering algorithm based on the kurtosis measure which, in related work, has been employed precisely for its channel independence. We compare ours to some recent algorithms through a standard validation procedure on simulated impulse responses. We show the proposed algorithm to deliver better results and, because it requires no channel-specific settings, is inherently robust to different environments. Results of the proposed algorithm are also illustrated on real measurements in four buildings with assorted wall materials.

Inversion of a room acoustics model for the determination of acoustical surface properties in enclosed spaces

Acoustic consultants are often in charge of treating spaces to fix problems or improve their room acoustics. To assess the situation and to find a solution, it is common practice to perform computer simulations. This technique is well established, cheap and effective. But it requires a CAD model of the room as well as properties of its boundaries, such as absorption and scattering coefficients. The CAD model is usually easy to obtain by asking the architect or measuring yourself, but quantifying the absorption and scattering coefficients of every single wall is a challenging task. This contribution presents a method that automatically matches absorption coefficients for every single wall by applying an inverse room acoustics model which bases on geometrical acoustics. The inversion is done numerically using a non-linear least-squares optimization process in MATLAB. The independent variables are all absorption coefficients and the goal is to minimize the error between measured and simulated impulse responses at all measured positions in the room. In addition to the acquisition of absorption and scattering coefficients, the goal after the optimization process is to perform interactive binaural auralizations that have a high perceptual congruence with the existing space.

Reducing confidence bands for simulated impulse responses

It is emphasized that the shocks in structural vector autoregressions are only identified up to sign and it is pointed out that this feature can result in very misleading confidence intervals for impulse responses if simulation methods such as Bayesian or bootstrap methods are used. The confidence intervals heavily depend on which variable is used for fixing the signs of the responses. In particular, when the shocks are identified via long-run restrictions the problem can be severe. It is pointed out that a suitable choice of variable for fixing the signs of the responses and, hence, of the shocks, can result in substantial reductions in the confidence bands for impulse responses.

Simulation of impulse response for indoor visible light communications using 3D CAD models

In this article, a tool for simulating the channel impulse response for indoor visible light communications using 3D computer-aided design (CAD) models is presented. The simulation tool is based on a previous Monte Carlo ray-tracing algorithm for indoor infrared channel estimation, but including wavelength response evaluation. The 3D scene, or the simulation environment, can be defined using any CAD software in which the user specifies, in addition to the setting geometry, the reflection characteristics of the surface materials as well as the structures of the emitters and receivers involved in the simulation. Also, in an effort to improve the computational efficiency, two optimizations are proposed. The first one consists of dividing the setting into cubic regions of equal size, which offers a calculation improvement of approximately 50% compared to not dividing the 3D scene into sub-regions. The second one involves the parallelization of the simulation algorithm, which provides a computational speed-up proportional to the number of processors used.

MEASUREMENT EVALUATION OF THE TGN RADIO CHANNEL MODELS USEFULNESS IN PREDICTING WLAN PERFORMANCE

The purpose of this paper is to discuss the applicability of the TGn radio channel models in estimating the performance of WLAN transmission. The speciflcity of the indoor radiowave propagation is flrst discussed, then TGn models are introduced together with a deterministic propagation model created by the authors for predicting the radio channel higher-order parameters. Intensive WLAN measurements have been carried out in two representative propagation environments and compared to theoretical predictions obtained in four conflgurations: beginning with the original TGN channel models, then enhancing them by including deterministically simulated pathloss and impulse responses and eventually by generating the channel impulse response on a purely random basis. The obtained results should indicate how accurately the general TGn channel models match measurements in real environments and how they compare to proposed successive modiflcations.

Rigid sphere room impulse response simulation: Algorithm and applications

Simulated room impulse responses have been proven to be both useful and indispensable for comprehensive testing of acoustic signal processing algorithms while controlling parameters such as the reverberation time, room dimensions, and source-array distance. In this work, a method is proposed for simulating the room impulse responses between a sound source and the microphones positioned on a spherical array. The method takes into account specular reflections of the source by employing the well-known image method, and scattering from the rigid sphere by employing spherical harmonic decomposition. Pseudocode for the proposed method is provided, taking into account various optimizations to reduce the computational complexity. The magnitude and phase errors that result from the finite order spherical harmonic decomposition are analyzed and general guidelines for the order selection are provided. Three examples are presented: an analysis of a diffuse reverberant sound field, a study of binaural cues in the presence of reverberation, and an illustration of the algorithm's use as a mouth simulator.

Reducing Confidence Bands for Simulated Impulse Responses

It is emphasized that the shocks in structural vector autoregressions are only identified up to sign and it is pointed out that this feature can result in very misleading confidence intervals for impulse responses if simulation methods such as Bayesian or bootstrap methods are used. The confidence intervals heavily depend on which variable is used for fixing the sign of the initial responses. In particular, when the shocks are identified via long-run restrictions the problem can be severe. It is pointed out that a suitable choice of variable for fixing the sign of the initial responses can result in substantial reductions in the confidence bands for impulse responses.

Real‐time auralization of wave simulation in complex three‐dimensional acoustic spaces.

A technique has been developed for modeling real‐time sound propagation in static acoustic spaces that relies on pre‐computed wave simulation. The associated system can auralize propagation that includes diffraction, interference, scattering and late reverberation, while supporting tens of moving point sources and moving listener in highly complex three‐dimensional scenes. Since direct storage of simulated impulse responses for runtime use is infeasible, a novel technique was developed to extract and compactly encode the perceptually salient information in the simulated band‐limited impulse responses. The response is automatically broken into early reflections (ERs) and late reverberation (LR), via a threshold on the temporal density of arriving wave‐fronts. The LR is simulated and stored once per room. Detailed spatial variation in ER is simulated, and encoded by a set of peak delays/amplitudes in the time domain and a residual frequency response sampled in octave bands, at each source/receiver point pai...

Design and Subspace System Identification of an Ex Vivo Vascular Perfusion System

Numerical algorithms for subspace system identification (N4SID) are a powerful tool for generating the state space (SS) representation of any system. The purpose of this work was to use N4SID to generate SS models of the flowrate and pressure generation within an ex vivo vascular perfusion system (EVPS). Accurate SS models were generated and converted to transfer functions (TFs) to be used for proportional integral and derivative (PID) controller design. By prescribing the pressure and flowrate inputs to the pumping components within the EVPS and measuring the resulting pressure and flowrate in the system,_four TFs were estimated;_two for a flowrate controller (H(RP,f) and H(RPP,f)) and two for a pressure controller (H(RP,p) and H(RPP,p)). In each controller,_one TF represents a roller pump (H(RP,f) and H(RP,p)),_and the other represents a roller pump and piston in series (H(RPP,f) and H(RPP,p)). Experiments to generate the four TFs were repeated five times (N=5) from which average TFs were calculated. The average model fits, computed as the percentage of the output variation (to_the_prescribed_inputs) reproduced by the model, were 94.93+/-1.05% for H(RP,p), 81.29+/-0.20% for H(RPP,p), 94.45+/-0.73% for H(RP,f), and 77.12+/-0.36% for H(RPP,f). The simulated step, impulse, and frequency responses indicate that the EVPS is a stable system and can respond to signals containing power of up to 70_Hz.

Listener-based Analysis of Surface Importance for Acoustic Metrics

Acoustic quality in room acoustics is measured by well defined quantities, like definition, which can be derived from simulated impulse response filters or measured values. These take into account the intensity and phase shift of multiple reflections due to a wave front emanating from a sound source. Definition (D50) and clarity (C50) for example correspond to the fraction of the energy received in total to the energy received in the first 50 ms at a certain listener position. Unfortunately, the impulse response measured at a single point does not provide any information about the direction of reflections, and about the reflection surfaces which contribute to this measure. For the visualization of room acoustics, however, this information is very useful since it allows to discover regions with high contribution and provides insight into the influence of all reflecting surfaces to the quality measure. We use the phonon tracing method to calculate the contribution of the reflection surfaces to the impulse response for different listener positions. This data is used to compute importance values for the geometry taking a certain acoustic metric into account. To get a visual insight into the directional aspect, we map the importance to the reflecting surfaces of the geometry. This visualization indicates which parts of the surfaces need to be changed to enhance the chosen acoustic quality measure. We apply our method to the acoustic improvement of a lecture hall by means of enhancing the overall speech comprehensibility (clarity) and evaluate the results using glyphs to visualize the clarity (C50) values at listener positions throughout the room.

Limited participation and exchange rate dynamics: Does theory meet the data?

The paper explores the empirical dimensions of a New Open Economy Macronomy model characterized by credit market frictions. We find that these frictions are essential for the model to match a large set of moments of German data. Moreover, the simulated impulse response functions to supply and nominal shocks are consistent with VAR findings. Since the model is estimated on moments rather than on conditional IRFs, this underlines the ability of the model to match the data. Finally, monetary shocks do not seem to be the primary driving force behind the aggregate dynamics, which is consistent with the VAR literature.

Modeling room impulse response by incorporating speaker polar response into image source method

Simple computer modeling of impulse responses for small rectangular rooms is typically based on the image source method, which results in an impulse response with very high time resolution. The image source method is easy to implement, but the simulated impulse responses are often a poor match to measured impulse responses because the description of the source is often too idealized to match the real measurement conditions. For example, the basic image source method has often assumed the sound source to be an omni‐directional point source for ease of implementation, but a real loudspeaker may include multiple drivers and exhibit an irregular polar response in both the horizontal and vertical directions. In this paper, an improved room impulse response computer modeling technique is developed by incorporating the measured horizontal and vertical polar responses of the speaker into the basic image source method. Results show that compared with the basic image source method, the modeled room impulse response using this method is a better match to the measured room impulse response.

Current impulse response of thin InP p+-i-n+ diodes using full band structure Monte Carlo method

A random response time model to compute the statistics of the avalanche buildup time of double-carrier multiplication in avalanche photodiodes (APDs) using full band structure Monte Carlo (FBMC) method is discussed. The effect of feedback impact ionization process and the dead-space effect on random response time are included in order to simulate the speed of APD. The time response of InP p+-i-n+ diodes with the multiplication region of 0.2μm is presented. Finally, the FBMC model is used to calculate the current impulse response of the thin InP p+-i-n+ diodes with multiplication lengths of 0.05 and 0.2μm using Ramo’s theorem [Proc. IRE 27, 584 (1939)]. The simulated current impulse response of the FBMC model is compared to the results simulated from a simple Monte Carlo model.

Influence of Deutlichkeit value and reverberation time on improved speech intelligibility in reverberant environments because of steady-state suppression

To improve speech intelligibility in reverberant environments, Arai et al. proposed ‘‘steady-state suppression (SSS)’’ as preprocessing [Arai et al., Acoust. Sci. Technol. 23, 229–232 (2002)]. In this study, a perceptual experiment under artificial reverberant conditions with simulated impulse responses was conducted to elucidate the effect of the Deutlichkeit (D) value and reverberation time (RT) on improvements of speech intelligibility because of SSS. Artificial impulse responses were simulated with white noise multiplied by a decay curve. The advantage of this method is that the simulated impulse responses have mutually similar frequency characteristics; consequently, we can evaluate them using only the D value and RT regardless of their different frequency characteristics. Two parameters, the energy of the impulse response 50 ms from the direct sound and the attenuation rate of the decay curve, were controlled to obtain several impulse responses having certain D value and RT. Results show that SSS improved speech intelligibility in the conditions of low D value, even if RT was long or short. We could also interpret these results as indicating that processing is effective when the original speech intelligibility is less than 60%. [Work supported by JSPS.KAKENHI (16203041).]

Optimal dispersion/dissipation-error finite-difference method for room impulse response simulation

The finite difference method is suitable for the calculation of acoustic impulse responses because of its computational simplicity and efficiency. However, for room acoustics applications, where reverberation makes it necessary to calculate the room impulse response and acoustic energy over a long duration, most standard finite-difference formulations are not practical because of the accumulation of dispersion and dissipation errors. In order to calculate very long impulse responses, a new, efficient, high-order finite-difference method is developed in this study. The new method is optimized to minimize the total dispersion and dissipation errors and hence the error accumulated in each time step resulting from discretization in both space and time. The error of the new method is significantly reduced so that the impulse response can be calculated over the whole reverberation time (about 1 to 3 s), using a relatively coarse spatial (6 grid points per wavelength) and a moderate temporal (CFL=1.0) resolutions. [Work supported by AFOSR.]

Current impulse response of thin InP p+–i–n+ diodes

The simulation of current impulse response using random response time model in avalanche photodiode (APD) is presented. A random response time model considers the randomness of times at which the primary and secondary carriers are generated in multiplication region. The dead-space effect is included in our model to demonstrate the impact on current impulse response of thin APDs. Current impulse response of homojunction InP p+–i–n+ diodes with the multiplication widths of 0.1 and 0.2μm are calculated. Our results show that dead-space gives a slower decay rate of current impulse response in thin APD, which may degrade the bit-error-rate of the optical communication systems.