Sources In Rooms Research Articles

A series of SNR-based speech intelligibility models in the Auditory Modeling Toolbox

This technical paper presents a series of speech intelligibility models that have been developed since the original version proposed by Lavandier and Culling [(2010). Journal of the Acoustical Society of America 127, 387–399]. This binaural model accounts for better-ear listening and binaural unmasking to predict the intelligibility of a near-field target speech among multiple stationary noise sources in rooms for normal-hearing listeners. Subsequent model versions allowed to consider a reverberated speech target in the far-field, envelope-modulated noise sources, and hearing-impaired listeners. As an intermediate step before considering speech maskers, a monaural version incorporating a harmonic-cancellation mechanism was recently developed to account for the effect of a stationary harmonic masker. This technical review is oriented towards model users and explains when and how each model should be used, points at its advantages and limitations, and provides an example of predictions using a data set from the literature. All these models along with the data, signals and code used to prepare the presented figures are made available within the Auditory Modeling Toolbox (AMT 1.1).

The role of early and late reflections on perception of source orientation.

Sound radiation of most natural sources, like human speakers or musical instruments, typically exhibits a spatial directivity pattern. This directivity contributes to the perception of sound sources in rooms, affecting the spatial energy distribution of early reflections and late diffuse reverberation. Thus, for convincing sound field reproduction and acoustics simulation, source directivity has to be considered. Whereas perceptual effects of directivity, such as source-orientation-dependent coloration, appear relevant for the direct sound and individual early reflections, it is unclear how spectral and spatial cues interact for later reflections. Better knowledge of the perceptual relevance of source orientation cues might help to simplify the acoustics simulation. Here, it is assessed as to what extent directivity of a human speaker should be simulated for early reflections and diffuse reverberation. The computationally efficient hybrid approach to simulate and auralize binaural room impulse responses [Wendt et al., J. Audio Eng. Soc. 62, 11 (2014)] was extended to simulate source directivity. Two psychoacoustic experiments assessed the listeners' ability to distinguish between different virtual source orientations when the frequency-dependent spatial directivity pattern of the source was approximated by a direction-independent average filter for different higher reflection orders. The results indicate that it is sufficient to simulate effects of source directivity in the first-order reflections.

Indoor Exposure to Selected Air Pollutants in the Home Environment: A Systematic Review.

(1) Background: There is increasing awareness that the quality of the indoor environment affects our health and well-being. Indoor air quality (IAQ) in particular has an impact on multiple health outcomes, including respiratory and cardiovascular illness, allergic symptoms, cancers, and premature mortality. (2) Methods: We carried out a global systematic literature review on indoor exposure to selected air pollutants associated with adverse health effects, and related household characteristics, seasonal influences and occupancy patterns. We screened records from six bibliographic databases: ABI/INFORM, Environment s, Pollution s, PubMed, ProQuest Biological and Health Professional, and Scopus. (3) Results: Information on indoor exposure levels and determinants, emission sources, and associated health effects was extracted from 141 studies from 29 countries. The most-studied pollutants were particulate matter (PM2.5 and PM10); nitrogen dioxide (NO2); volatile organic compounds (VOCs) including benzene, toluene, xylenes and formaldehyde; and polycyclic aromatic hydrocarbons (PAHs) including naphthalene. Identified indoor PM2.5 sources include smoking, cooking, heating, use of incense, candles, and insecticides, while cleaning, housework, presence of pets and movement of people were the main sources of coarse particles. Outdoor air is a major PM2.5 source in rooms with natural ventilation in roadside households. Major sources of NO2 indoors are unvented gas heaters and cookers. Predictors of indoor NO2 are ventilation, season, and outdoor NO2 levels. VOCs are emitted from a wide range of indoor and outdoor sources, including smoking, solvent use, renovations, and household products. Formaldehyde levels are higher in newer houses and in the presence of new furniture, while PAH levels are higher in smoking households. High indoor particulate matter, NO2 and VOC levels were typically associated with respiratory symptoms, particularly asthma symptoms in children. (4) Conclusions: Household characteristics and occupant activities play a large role in indoor exposure, particularly cigarette smoking for PM2.5, gas appliances for NO2, and household products for VOCs and PAHs. Home location near high-traffic-density roads, redecoration, and small house size contribute to high indoor air pollution. In most studies, air exchange rates are negatively associated with indoor air pollution. These findings can inform interventions aiming to improve IAQ in residential properties in a variety of settings.

Investigation of Auditory Objects Caused by Directional Sound Sources in Rooms

Investigation of Auditory Objects Caused by Directional Sound Sources in Rooms

Estimation of scattering contribution in the calibration of neutron devices with radionuclide sources in rooms of different sizes

Calibrations of neutron devices used in area monitoring are often performed by radionuclide neutron sources. Device readings increase due to neutrons scattered by the surroundings and the air. The influence of said scattering effects have been investigated in this paper by performing Monte Carlo simulations for ten different radionuclide neutron sources inside several sizes of concrete wall spherical rooms (Rsp = 200 to 1500 cm). In order to obtain the parameters that relate the additional contribution from scattered neutrons, calculations using a polynomial fit model were evaluated. Obtained results show that the contribution of scattering is roughly independent of the geometric shape of the calibration room. The parameter that relates the room-return scattering has been fitted in terms of the spherical room radius, so as to reasonably accurately estimate the scattering value for each radionuclide neutron source in any geometry of the calibration room.

The role of diffusive architectural surfaces on auditory spatial discrimination in performance venues

In musical or theatrical performance, some venues allow listeners to individually localize and segregate individual performers, while others produce a well blended ensemble sound. The room acoustic conditions that make this possible, and the psycho-acoustic effects at work are not fully understood. This research utilizes auralizations from measured and simulated performance venues to investigate spatial discrimination of multiple acoustic sources in rooms. Signals were generated from measurements taken in a small theater, and listeners in the audience area were asked to distinguish pairs of speech sources on stage with various spatial separations. This experiment was repeated with the proscenium splay walls treated to be flat, diffusive, or absorptive. Similar experiments were conducted in a simulated hall, utilizing 11 early reflections with various characteristics, and measured late reverberation. The experiments reveal that discriminating the lateral arrangement of two sources is possible at narrower separation angles when reflections come from flat or absorptive rather than diffusive surfaces.

Binaural prediction of speech intelligibility in reverberant rooms with multiple noise sources

When speech is in competition with interfering sources in rooms, monaural indicators of intelligibility fail to take account of the listener's abilities to separate target speech from interfering sounds using the binaural system. In order to incorporate these segregation abilities and their susceptibility to reverberation, Lavandier and Culling [J. Acoust. Soc. Am. 127, 387-399 (2010)] proposed a model which combines effects of better-ear listening and binaural unmasking. A computationally efficient version of this model is evaluated here under more realistic conditions that include head shadow, multiple stationary noise sources, and real-room acoustics. Three experiments are presented in which speech reception thresholds were measured in the presence of one to three interferers using real-room listening over headphones, simulated by convolving anechoic stimuli with binaural room impulse-responses measured with dummy-head transducers in five rooms. Without fitting any parameter of the model, there was close correspondence between measured and predicted differences in threshold across all tested conditions. The model's components of better-ear listening and binaural unmasking were validated both in isolation and in combination. The computational efficiency of this prediction method allows the generation of complex "intelligibility maps" from room designs.

Attentional tracking in real-room reverberation.

A listener can attend to one talker in a mixture of sound sources, and a difference in bearing between “target” and interfering sources is thought to aid this “tracking.” Interaural cues are degraded by reverberation however, raising the question of what cues are actually used to track sources in rooms? Listeners can also use differences in voice characteristics, so this study asks how well cues arising from location compete with talker differences when tracking messages in real-room reverberation. Real room measurements of binaural room impulse responses (BRIRs) were used to spatialize the stimuli and listeners decided which of two simultaneous target words belonged in a target phrase played simultaneously with a “distracter” phrase. Location differences were in competition with talker differences so that listeners’ responses indicated which cue-type they were tracking. Further experiments used processed BRIRs to eliminate temporal cues. Location was dominant over talker difference in dichotic but not diotic conditions, and results with processed BRIRs indicated that this “binaural advantage” is almost entirely due to ILD. Furthermore, an analysis of spectral distances between BRIR channels revealed that the probability of location difference overriding talker difference correlates with the distance between ILD patterns but not with monaural spectral distances.

Localization of sound sources in rooms using an improved version of steered response power algorithm.

Localization of sound sources inside a room is a challenging problem. The possible applications involving speech‐based source localization systems range from teleconferencing to home automation systems. For example, the localization of a speaker inside a conference room can be very useful to place the speaker in a remote room by means of a spatial audio reproduction system. Also, new applications will appear in home automation if accurate source localization systems are available in the future. One of the most robust approaches to source localization is the SRP‐PHAT algorithm, which has shown to provide very good localization results inside rooms with moderate reverberation. However, the computational cost is highly dependent on the spatial sampling and the number of microphones, making very difficult the localization of sound events if a coarse spatial sampling is used. In this paper, we propose an improvement of this method where sound events are not missed even if a very coarse grid is used. The improvement is based on a previous calculation of the existent cross‐correlation lags between spatially adjacent points in the grid, assuring that the non‐sampled space is covered in terms of cross‐correlation lags between microphone pairs when running the algorithm. Several experiments conducted in different rooms with complex acoustics confirm the validity and benefits of the proposed method.

A system to simulate and reproduce audio–visual environments for spatial hearing research

The article reports the experience gained from two implementations of the “Simulated Open-Field Environment” (SOFE), a setup that allows sounds to be played at calibrated levels over a wide frequency range from multiple loudspeakers in an anechoic chamber. Playing sounds from loudspeakers in the free-field has the advantage that each participant listens with their own ears, and individual characteristics of the ears are captured in the sound they hear. This makes an easy and accurate comparison between various listeners with and without hearing devices possible. The SOFE uses custom calibration software to assure individual equalization of each loudspeaker. Room simulation software creates the spatio-temporal reflection pattern of sound sources in rooms which is played via the SOFE loudspeakers. The sound playback system is complemented by a video projection facility which can be used to collect or give feedback or to study auditory–visual interaction. The article discusses acoustical and technical requirements for accurate sound playback against the specific needs in hearing research. An introduction to software concepts is given which allow easy, high-level control of the setup and thus fast experimental development, turning the SOFE into a “Swiss army knife” tool for auditory, spatial hearing and audio–visual research.

Subjective evaluation of auralizations created from multi-channel anechoic recordings of a talker in motion

A high degree of speech intelligibility is very important in educational environments. When designing such spaces, like classrooms, auralizations can be used to subjectively assess the degree of speech intelligibility and clarity. Auralizations are most commonly made by convolving the impulse response (IR) of an omni-directional source with a single channel anechoic speech recording. This paper explores the idea of using multi-channel recordings to create the auralizations, using a female talker in motion. An omni-directional source is split into quadrants and the IR is calculated for each section. These IR’s are convolved with the appropriate channel of the anechoic recording and then the four auralizations are mixed to create one final auralization. The auralizations were made using four-channel anechoic recordings of a person walking on a platform while talking. Subjective tests were conducted to determine the ease with which subjects could identify the direction of the movement of the source in rooms with varying amounts of absorption. This method can be used to create more realistic classroom auralizations, as teachers typically move around the room as they teach. [Work supported by the National Science Foundation.]

Adaptive separation of acoustic sources for anechoic conditions: A constrained frequency domain approach

Blind source separation represents a signal processing technique with a large potential for noise reduction. However, its application in modern digital hearing aids poses high demands with respect to computational efficiency and speed of adaptation towards the desired solution. In this paper, an algorithm is presented which fulfills these goals under the idealized assumption that the superposition of sources in rooms can be approximated as a superposition under anechoic conditions. Specifically, attenuation, the signals’ finite propagation speed, and diffuse noise are accounted for, whereas reflections and reverberation are considered as negligible effects. This approximation is referred to as the ‘free field’ assumption. Starting from a general blind source separation algorithm for Fourier transformed speech signals, the free field assumption is incorporated into the framework, yielding a simple, fast and adaptive algorithm that is able to track moving sources. Implementation details are given which were found to be indispensable for fast and robust signal separation. Performance is evaluated both by simulations and experimentally, including separation of a moving and a fixed speaker in a recorded real anechoic environment. The potential benefits and shortcomings of this algorithm are discussed with regard to its inclusion into the signal processing framework of digital hearing aids for real reverberant acoustic situations.

Active source location and beamforming

A fundamental problem in designing user interfaces that incorporate speech and vision is locating the user(s) and enhancing the quality of their speech. We present a novel algorithm for actively doing this. Two complementary coarse-to-fine strategies that divide both the space being searched and the received signal in the frequency domain are used to arrive at an efficient dynamic search algorithm that is capable of both locating and beamforming multiple sources distributed in space. The algorithm makes no assumptions on noise statistics, and has a deterministic performance bound. It is able to make use of prior information on the possible location of sources obtained via means such as video. The algorithm is particularly applicable to locating speech sources in rooms of regular size, and is thus suitable for videoconferencing and user-interface applications. The algorithm and details are presented. [Support from the W. M. Keck Foundation and ONR Contract No. N000149510521 is gratefully acknowledged.]

Evaluation of sound insulation materials in a reverberant field by the sound intensity method

Sound intensity is a vector quantity possessing magnitude and direction. It is an effective means of studying the power level of sound sources in rooms with background noise, and sound transmission through soundproof structures. However, it was believed that it was not possible to use the sound intensity method in diffused sound fields, for both theoretical and practical reasons. To determine whether it was possible to measure sound intensity in a reverberation chamber forming an artificial sound diffusing field, the transmission loss through sound insulating materials was measured. A comparison with the reverberation method, specified in Japan Industrial Standards (JIS), indicated that the results are almost identical. This technique also substantially reduces the measuring time, making it more economical than the conventional method. The limits of measurement in a diffused sound field were also determined.