Room Acoustic Parameters Research Articles

Proportion of effects by head-related transfer function and receiver position variation to interaural cross-correlation values.

Interaural cross-correlation coefficient (IACC) is an objective room-acoustic parameter associated with the spatial impression and subjective quality of the acoustics. This study investigates the proportion of effects on the IACC variance simultaneously by (1) varied head-related transfer function (HRTF) and (2) locally varied receiver positions. The early IACC80 values are estimated from the binaural room simulations in eight room-acoustic conditions varying in room shape, side wall absorption, and receiver distance. Analysis across the combinations of HRTF and receiver positions indicates that below 2 kHz, around two-thirds of total IACC variance is explained by the receiver displacement, and at higher frequencies the HRTF variations dominate the IACC variance.

The effect of different acoustical treatment in a classroom

A common room acoustic measure in classrooms and other common public spaces is a suspended sound absorbing ceiling. However, the acoustical condition in the classroom not only depends on the suspended ceiling. The size and shape of the room as well as the properties of building material and the interior fittings and furniture will also affect the room acoustical conditions. Another circumstance is the non-fulfillment of the conditions for the classic diffuse field theory in rooms with absorbent ceiling treatment due to the non-uniform distribution of the absorbing material. This makes the calculation of room acoustic parameters more complex. This paper addresses the effect of different factors that are of importance for the acoustical conditions in a classroom. Outgoing from the unfurnished classroom without suspended ceiling the effect of introducing a suspended ceiling, adding furniture, adding wall panels, as well as extra low frequency absorption will be exemplified based on measurements in a full scale classroom. The room acoustic parameters that are analyzed are the reverberation time T20, the Speech Clarity C50 and the Sound Strength G. A calculation model adapted for the non-diffuse conditions in rooms with ceiling treatment will be briefly mentioned.

First international round robin on auralization: Results of the acoustical evaluation

The first round robin on auralization allows developers of room acoustical simulation software to provide results of their simulation model for typical scenarios of sound propagation and room acoustics. In contrast to the past round robins on room acoustics simulation, it includes a perceptual evaluation of the simulation results in addition to the evaluation based on room impulse responses and room acoustic parameters. In this talk, we will present the acoustical analysis of the monaural simulation results, based on differences in the temporal and spectral features of the transfer function as well as differences in standard room acoustical parameters for the nine scenes of the round robin. These indicate shortcomings in the corresponding simulation algorithms, provide indications which effects and which acoustical situations are particularly challenging for the different simulation approaches, and predict potential perceptual differences in the listening tests.

Comparative analysis of absorption coefficients’ effect on room acoustic parameters determined by simulation software

A comparative analysis between different sets of absorption coefficients, found or calculated from a variety of sources and methods, including traditional databases and newer in-situ methods, was carried out. This analysis utilized different architectural acoustic simulation software packages for verification of results and further comparison. Initially, a shoebox model was compared for reference and brief comparison between the software packages was made. Then, the main analysis was conducted using the model of the RWTH Aachen Institute of Technical Acoustics’ Seminar Room. This room was simulated with all the different sets of absorption coefficients through both simulation software packages. The purpose of this analysis was to provide a reference for the variation of room acoustic parameters from the different sources of absorption coefficients.

Omnidirectional measurement of room impulse response using a small bookshelf loudspeaker as a sound source

A dodecahedral loudspeaker is commonly used in room acoustical measurements as an omnidirectional sound source. However, inverse filtering to obtain an ideal room impulse response (RIR) is not easy because of its irregular frequency and temporal characteristics. When this RIR is convolved with music signals, the reproduced sound does not possess adequate fidelity to evaluate the acoustical quality of the concert hall. Hence a new measurement method of the RIR by an omnidirectional source is proposed: RIR’s are measured by a small bookshelf loudspeaker rotating around its acoustic center in multiple directions, and the RIR’s are averaged to obtain omnidirectional response. Physical characteristics of the RIR determined with this procedure are given and the room acoustical parameters are compared with those by the dodecahedral method. Finally, application to subjective experiments is described.

Multidimensional scaling approach in room acoustic evaluation

In the event of natural acoustics recordings, it is essential to decide on the room and, consequently, on the reverb. The decision is very important, as the consequences are not possible to be changed in the process of mixing. Therefore, proper selection of the parameter is often essential to achieve the effect desired. The aim of the study is an attempt to answer the question what is the optimal or preferred by an average listener reverberation time and other room acoustic parameters in choral music. As part of the study, sound samples of choral music that differed only by the reverb were made. The samples were tested using the procedures of multidimensional scaling. Ambisonics, altogether with VBAP, was used in the listening test.

Triton: Practical pre-computed sound propagation for games and virtual reality

Triton is a pre-computed wave-based acoustics system recently shipped in the game “Gears of War 4.” Games and VR present exciting new opportunities for virtual acoustics by providing the player with scene-dependent reverberation cues and conveying information about visually occluded areas. Several technical challenges must be met. Scenes containing millions of polygons are common, with mixed indoor-outdoor spaces like broken buildings, courtyards, caves, and rocks. A viable technique must handle this complex visual geometry without users' intervention. The emphasis is on ensuring the resulting auralization is perceptually convincing, varying smoothly on source and listener motion in such scenes. Highly occluded cases with salient paths undergoing multiple edge-diffraction and scattering are common. Computational requirements are quite stringent. A fraction of a single CPU core must be used for acoustic calculations for many tens of moving sources. We discuss how these challenges shape Triton’s design. Pre-computation is used to minimize runtime cost. Wave simulation provides complete automation for complex scene geometry. The produced fields contain billions of responses that take terabytes of memory. A key contribution is compact encoding of this data in less than hundred megabytes: objective room acoustic parameters are approached from a novel perspective to aid in spatial compression. The resulting parametric framework is fast and practical for current games and VR applications. Video demonstrations will be shown.

First international round robin on auralization: Results of the perceptual evaluation

The round robin on auralization aimed at a systematic evaluation of room acoustic modeling software by means of comparing simulated and measured impulse responses. While a physical evaluation by means room acoustical parameters and spectro-temporal comparisons is addressed in an accompanying talk, here, we focus on an evaluation of perceptual differences arising in complex room acoustical scenarios. In these cases, a mere physical evaluation might not be able to predict the perceptual impact of the manifold interaction of different sound propagation phenomena in enclosed spaces such as reflection, scattering, diffraction, or modal behavior. For this purpose, dynamic auralizations of binaural room impulse responses that were simulated with different room acoustical modeling softwares were evaluated against their measured counterparts. For this purpose, listening tests were conducted using “plausibility” and “authenticity” as overall quality criteria and the Spatial Audio and Quality Inventory (SAQI) for a differential diagnosis of the remaining differences.

Noise disturbance in open-plan study environments: a field study on noise sources, student tasks and room acoustic parameters

The aim of this study is to gain more insight in the assessment of noise in open-plan study environments and to reveal correlations between noise disturbance experienced by students and the noise sources they perceive, the tasks they perform and the acoustic parameters of the open-plan study environment they work in. Data were collected in five open-plan study environments at universities in the Netherlands. A questionnaire was used to investigate student tasks, perceived sound sources and their perceived disturbance, and sound measurements were performed to determine the room acoustic parameters. This study shows that 38% of the surveyed students are disturbed by background noise in an open-plan study environment. Students are mostly disturbed by speech when performing complex cognitive tasks like studying for an exam, reading and writing. Significant but weak correlations were found between the room acoustic parameters and noise disturbance of students.Practitioner Summary: A field study was conducted to gain more insight in the assessment of noise in open-plan study environments at universities in the Netherlands. More than one third of the students was disturbed by noise. An interaction effect was found for task type, source type and room acoustic parameters.

Predicting the perceived reverberation in different room acoustic environments using a binaural auditory model.

In this paper a binaural auditory model was used to compute reverberance estimates in four simulated halls. For three of the halls different absorption conditions were evaluated. The model estimates (pRev) were obtained using music excerpts of an orchestra consisting of 23 instrument sections and then compared with the room acoustic parameters of reverberation time (T30) and early decay time (EDT) at mid frequencies. Although the results showed that pRev has a higher correlation with EDT rather than with T30, this relationship depends on the properties of the instruments. The simulations show that pRev depends on the presentation level and that for instruments with similar critical-band spectrum, pRev follows a similar trend across acoustic conditions. A computational framework and sound stimuli are provided to encourage the search of experimental evidence of the aspects addressed in this study.

EVALUATION OF THE REVERBERATION TIME IMPROVEMENT IN A SPEAKING HALL

To improve a room's acoustic parameters there have been studied several variants of acoustic materials and devices that can be placed on the ceiling of the hall. The main objective of the study was the reverberation time measurement and calculation. By using the acoustic panel made from polystyrene, covered with jute on the both sides, has ensured the largest reverberation time decrease. Thus, we can say that the analyzed room can be used for speech activity (courses, conferences etc.)

Perception of music dynamics in concert hall acoustics.

Dynamics is one of the principal means of expressivity in Western classical music. Still, preceding research on room acoustics has mostly neglected the contribution of music dynamics to the acoustic perception. This study investigates how the different concert hall acoustics influence the perception of varying music dynamics. An anechoic orchestra signal, containing a step in music dynamics, was rendered in the measured acoustics of six concert halls at three seats in each. Spatial sound was reproduced through a loudspeaker array. By paired comparison, naive subjects selected the stimuli that they considered to change more during the music. Furthermore, the subjects described their foremost perceptual criteria for each selection. The most distinct perceptual factors differentiating the rendering of music dynamics between halls include the dynamic range, and varying width of sound and reverberance. The results confirm the hypothesis that the concert halls render the performed music dynamics differently, and with various perceptual aspects. The analysis against objective room acoustic parameters suggests that the perceived dynamic contrasts are pronounced by acoustics that provide stronger sound and more binaural incoherence by a lateral sound field. Concert halls that enhance the dynamics have been found earlier to elicit high subjective preference.

Preference of reverberation time for musicians and audience of the Javanese traditional gamelan music

This paper presents results of an investigation of room acoustic parameters those are appropriated particularly to perform a Javanese gamelan. The acoustic parameters were obtained by analysing simulated sounds of performance. Those simulated sounds were obtained by sound convolution technique of a dry sound signal of Javanese gamelan performance with impulse responses rooms whose appropriated reverberation time. The reverberation time were varied between 1.0s to 1.8s, those belong to the characteristic of Pendopo Mangkunegaran Surakarta. In this case, Pendopo Mangkunegaran is assumed as one of the most suitable concert halls for Javanese gamelan performance.To obtain the acoustic parameters, we used a psycho-acoustics measurement based on paired comparison test that having different of acoustic parameters to determine the most comfortable one to majority of respondents. The respondents who have participated in this research composed of a group of professional musicians of Javanese gamelan and groups of audience who are not musician, nevertheless part of them were familiar with Javanese gamelan music.The comparison test gave results and showed majority of respondents of group of musicians had a notion sound reverberation time of 1.2s was most comfortable. This corresponds to +6.2dB, clarity and 74% definition. It means the appropriate acoustic condition allows musicians to recognize and distinguish clearly sound of each instrument being played. Meanwhile, group of audience had a notion reverberation time in a range of 1.2s - 1.6s was most comfortable. This range of reverberation time corresponds to +4dB to +6.2dB of clarity, and 66% to 74% of definition.

Subjective evaluation of sound diffusion in a surround hall

The effects of diffusing elements on sound field diffuseness were investigated by subjective evaluations using binaural impulse responses (BIRs) in seating areas in a surround hall. The room acoustical parameters as well as the number of peaks (Np) and local maxima within -20 dB of the amplitude of direct sound were investigated to evaluate the diffuseness in the halls. For the listening test, stimuli were selected to explore the combination of acoustic parameters and degree of diffusion. The music signals were convolved with the measured BIRs in different listening positions. Based on the listening test, it was found that positions close to the diffusers with a high scattering coefficient were preferred by the listeners.

Characterization of the acoustic quality of classrooms in a music education facility

Classrooms of a music education facility were characterized by the user by means of a questionnaire study and by acoustic impulse response measurements and subsequent calculation of reverberation time, definition, and other room acoustics parameters. The questionnaire study enabled to understand the preferences of students and music teachers regarding the acoustic quality of a total of twenty rooms for music practice and teaching. It was observed that preference for a certain room also depends on the instrument mostly played by the user. Three study rooms and three collective classrooms were the most cited ones and these have been evaluated according to ISO 3382. Opinions of the musicians showed to be coherent with the measurement data as the rooms considered to be dry had reverberation times around 0.3 seconds, and the rooms considered to be reverberant had reverberation times around 1.5 seconds. The six classrooms that were characterized as clear and well defined rooms, showed values for Clarity around 1 dB for live rooms and 14 to 22 dB for dry rooms. Definition remained above 43% for all rooms with Central Time below 24 ms for clarity rooms and less reverberant, and above 98 ms for the live rooms.

Perceptually plausible acoustics simulation of single and coupled rooms

The fast and perceptually plausible room acoustics simulator [RAZR, see Wendt et al., JAES 62, 11 (2014)] has been optimized and extended to simulate the acoustics of connected rooms. RAZR synthesizes binaural room impulse responses (BRIRs) with high computational efficiency using a hybrid approach: early reflections are calculated as image sources for a shoebox-room approximation up to a low order, and the later reverberation is generated by a binaurally extended feedback delay network (FDN). For the extension toward two coupled rooms, validity, visibility, and diffraction of the image sources in the two rooms were taken into account, as well as different reverberation properties and the opening angle of the door to the neighbor room seen from a specific receiver position. The suggested method was evaluated by comparing measured and synthesized BRIRs for several rooms differing in size and reverberation time. For room acoustical parameters such as early decay time, late decay time, definition, and clarity a good agreement in terms of the Pearson correlation coefficient (0.86—0.99) was achieved between measured and simulated BRIRs. Subjective listening tests showed a good agreement of ratings of perceptual attributes (e.g., tone-color, reverberation time, envelopment, and naturalness) for the measured and synthesized BRIRs.

ROOM MATERIAL IDENTIFICATION SYSTEM FROM PHOTO IMAGES USING GLCM, MODIFIED ZERNIKE MOMENTS, AND PSO-BP APPLICATION

In acoustic engineering, the types of material used in a room are basically one of the fundamental features that are essential in some of room acoustic parameters computation. This paper proposed an improved system to identify room material type from its surface photographic image. Data images of several room surfaces were collected for the system input. This improved system implements Gray Level Co-occurrence Matrix (GLCM) and modified Zernike moments for image extraction and hybrid Particle Swarm Optimization and back-propagation (PSO-BP) algorithm for classification. For comparison purpose, experiments using variations combination of GLCM and modified Zernike moments extraction as well as Levenberg-Marquardt, back-propagation neural network (BPNN), and PSO-BP algorithm were executed. By applying the proposed methods, the system accuracy increased around 30% compared to previous research. Moreover, the convergence attained during training was three times faster compared to BP algorithm. Thus using the new methods in identifying material surface images had positively improved the system in becoming more efficient and reliable.

Speech intelligibility of English, Polish, Arabic and Mandarin under different room acoustic conditions

This paper examines the impact of room acoustic conditions on the speech intelligibility of four languages (English, Polish, Arabic and Mandarin). Listening test scores (diagnostic rhyme tests, phonemically balanced word tests and phonemically balanced sentence tests) of the four languages were compared under four room acoustic conditions defined by their speech transmission index (STI=0.2, 0.4, 0.6 and 0.8). The results obtained indicated that there was a statistically significant difference between the word intelligibility scores of languages under all room acoustic conditions, apart from the STI=0.8 condition. English was the most intelligible language under all conditions, and differences with other languages were larger when conditions were poor (maximum difference of 29% at STI=0.2, 33% at STI=0.4 and 14% at STI=0.6). Results also showed that Arabic and Polish were particularly sensitive to background noise, and that Mandarin was significantly more intelligible than those languages at STI=0.4. Consonant-to-vowel ratios and languages’ distinctive features and acoustical properties explained some of the scores obtained. Sentence intelligibility scores confirmed variations between languages, but these variations were statistically significant only at the STI=0.4 condition (sentence tests being less sensitive to very good and very poor room acoustic conditions). Overall, the results indicate that large variations between the speech intelligibility of different languages can occur, especially for spaces that are expected to be challenging in terms of room acoustic conditions. Recommendations solely based on room acoustic parameters (e.g. STI) might then prove to be insufficient for designing a multilingual environment.

Spatial Acoustic Scenarios in Multichannel Loudspeaker Systems for Hearing Aid Evaluation.

Field tests and guided walks in real environments show that the benefit from hearing aid (HA) signal processing in real-life situations is typically lower than the predicted benefit found in laboratory studies. This suggests that laboratory test outcome measures are poor predictors of real-life HA benefits. However, a systematic evaluation of algorithms in the field is difficult due to the lack of reproducibility and control of the test conditions. Virtual acoustic environments that simulate real-life situations may allow for a systematic and reproducible evaluation of HAs under more realistic conditions, thus providing a better estimate of real-life benefit than established laboratory tests. To quantify the difference in HA performance between a laboratory condition and more realistic conditions based on technical performance measures using virtual acoustic environments, and to identify the factors affecting HA performance across the tested environments. A set of typical HA beamformer algorithms was evaluated in virtual acoustic environments of different complexity. Performance was assessed based on established technical performance measures, including perceptual model predictions of speech quality and speech intelligibility. Virtual acoustic environments ranged from a simple static reference condition to more realistic complex scenes with dynamically moving sound objects. HA benefit, as predicted by signal-to-noise ratio (SNR) and speech intelligibility measures, differs between the reference condition and more realistic conditions for the tested beamformer algorithms. Other performance measures, such as speech quality or binaural degree of diffusiveness, do not show pronounced differences. However, a decreased speech quality was found in specific conditions. A correlation analysis showed a significant correlation between room acoustic parameters of the sound field and HA performance. The SNR improvement in the reference condition was found to be a poor predictor of HA performance in terms of speech intelligibility improvement in the more realistic conditions. Using several virtual acoustic environments of different complexity, a systematic difference in HA performance between a simple reference condition and more realistic environments was found, which may be related to the discrepancy between laboratory and real-life HA performance reported previously.

EVALUATION OF THE REVERBERATION TIME IMPROVEMENT IN A SPEAKING HALL

To improve a room's acoustic parameters there have been studied several variants of acoustic materials and devices that can be placed on the ceiling of the hall. The main objective of the study was the reverberation time measurement and calculation. By using the acoustic panel made from polystyrene, covered with jute on the both sides, has ensured the largest reverberation time decrease. Thus, we can say that the analyzed room can be used for speech activity (courses, conferences etc.)