Academic literature on the topic 'Optimal reverberation time'

We address the measurement of reverberation in terms of the (DRR) in the context of the assessment of dereverberation algorithms for which we wish to quantify the level of reverberation before and after processing. The DRR is normally calculated from the impulse response of the reverberating system. However, several important dereverberation algorithms involve nonlinear and/or time-varying processing and therefore their effect cannot conveniently be represented in terms of modifications to the impulse response of the reverberating system. In such cases, we show that a good estimate of DRR can be obtained from the input/output signals alone using the Signal-to-Reverberant Ratio (SRR) only if the source signal is spectrally white and correctly normalized. We study alternative normalization schemes and conclude by showing a least squares optimal normalization procedure for estimating DRR using signal-based SRR measurement. Simulation results illustrate the accuracy of DRR estimation using SRR.

The objective of this study was to use auralization techniques to investigate the optimal reverberation for speech intelligibility for normal-hearing and hearing-impaired adult listeners in classrooms with non-diffuse sound fields. This extended a previous study involving rooms with diffuse sound fields to more realistic rooms. Modified Rhyme Test (MRT) signals were auralized in six virtual classroom configurations with different reverberation times. Each classroom contained a speech source, a listener at a receiver position, and a noise source located between the talker and the listener. Two speech- and noise-source output-level differences (0 and +4 dB) were tested. Subjects performed speech-intelligibility tests in the virtual classrooms to identify the reverberation time that gave the best results in each case. For both normal and hearing-impaired listeners, the optimal reverberation time was generally non-zero, and increased with decreased speech-to-noise level difference. Hearing-impaired subjects apparently required more early energy than normal-hearing subjects. The optimal reverberation time for speech intelligibility in classrooms is not necessarily zero, as is commonly believed. The optimal value is generally non-zero, and varies with the room, the locations of the speech and noise sources and the listener, and the noise level.

This paper presents a novel scheme for speech dereverberation. The core of our method is a two-stage single-channel speech enhancement scheme. Degraded speech obtains a sparser representation of the linear prediction residual in the first stage of our proposed scheme by applying orthogonal matching pursuit on overcomplete bases, trained by the K-SVD algorithm. Our method includes an estimation of reverberation and mixing time from a recorded hand clap or a simulated room impulse response, which are used to create a time-domain envelope. Late reverberation is suppressed at the second stage by estimating its energy from the previous envelope and removed with spectral subtraction. Further speech enhancement is applied on minimizing the background noise, based on optimal smoothing and minimum statistics. Experimental results indicate favorable quality, compared to two state-of-the-art methods, especially in real reverberant environments with increased reverberation and background noise.

The generalized spectral subtraction algorithm (GBSS), which has extraordinary ability in background noise reduction, is historically one of the first approaches used for speech enhancement and dereverberation. However, the algorithm has not been applied to de-noise the room impulse response (RIR) to extend the reverberation decay range. The application of the GBSS algorithm in this study is stated as an optimization problem, that is, subtracting the noise level from the RIR while maintaining the signal quality. The optimization process conducted in the measurements of the RIRs with artificial noise and natural ambient noise aims to determine the optimal sets of factors to achieve the best noise reduction results regarding the largest dynamic range improvement. The optimal factors are set variables determined by the estimated SNRs of the RIRs filtered in the octave band. The acoustic parameters, the reverberation time (RT), and early decay time (EDT), and the dynamic range improvement of the energy decay curve were used as control measures and evaluation criteria to ensure the reliability of the algorithm. The de-noising results were compared with noise compensation methods. With the achieved optimal factors, the GBSS contributes to a significant effect in terms of dynamic range improvement and decreases the estimation errors in the RTs caused by noise levels.

The noise effects in the room impulse response (RIR) make the decay range of the integrated impulse response insufficient for reliable determination of reverberation time (RT). One of the preferred techniques to minimize noise effects is based on noise subtraction, RIR truncation, and correction for the truncation. The success of RT estimation through the method depends critically on the accurate estimation of the truncation time (TT). However, noise fluctuation and RIR irregularities can lead to discrepancies in the determined TT from the optimal value. The general goal of this paper is to improve RT estimates. An iterative procedure based on a non-exponential decay model consisting of a double-slope decay term and a noise term is presented to estimate the TT accurately. The model parameters are generated until the iterative procedure converges to a minimum difference between the energy decay curve (EDC) generated by the model and the Schroeder decay function. The decay rates of the EDCs with added pink noise levels are compared to those of the EDCs with low background noise. In addition, the detected TTs and the corresponding RTs are compared with the existing method and the noise compensation method (subtraction–truncation–correction method).

To extract the intrinsic bottom back-scattering information from the reverberation data in shallow water has been a challenge topic for long time. It is shown that the modal back-scattering matrix (MBSM) is the intrinsic description of the bottom scattering.1 The optimum source-depth distribution for inverting MBSM from the reverberation data has been discussed with a Pekeris waveguide.2 In the present work, we extend the procedure to the general case of non-Pekeris waveguide by using the simulated annealing (SA) approach. Numerical simulated examples on searching the optimum source-depth distribution for MBSM inversion are presented. It is shown that: (1) the SA is an effective approach for searching the optimum source-depth distribution for MBSM inversion (2) the MBSM inverted from the optimal source-depth distribution has the strong stability against noise.

A set of experimental studies is carried out to determine the acoustic characteristics of three-dimensional panels of fixed thickness made of carbon-based composite material installed in the opening between the reverberation chambers. Sound insulation indices are determined when they are excited by a diffuse sound field in wide frequency ranges. The reverberation time in model chambers with different partition configurations is calculated. The optimal configuration of the partition with pyramidal cells to reduce the reverberation time in the rooms is determined. The use of graphite in the form of thin membrane applied to various surfaces can significantly reduce the sound pressure levels in the room and increase the sound insulation indices of air noise. In addition to thin membrane, graphite can be used as an additive in composite materials for sound insulation purposes. It is shown that the characteristics of such panels are quite universal. The measured acoustic characteristics of composite panels are compared with similar characteristics of traditional materials. It is determined that the composition belongs to the I group of fire-retardant efficiency and can be recommended for use as a fire-retardant material. The developed acoustic material is an effective absorbing agent that solves problems in architectural acoustics, echo cancellation in construction and architecture. Similar to metamaterials, natural and artificial graphites allow to solve these problems with small volumes and masses using simple and inexpensive technologies.

Handclap is a convenient and useful acoustic source. This study aimed to explore its optimal application and limitations for acoustic measurements as well for other possible utilizations. For this purpose, the following steps were performed: investigation of the optimal hand configuration for acoustic measurements and measurements at different microphone source distances and at different spaces and positions. All measurements were performed with a handclap and a dodecahedron speaker for comparison. The results indicate that the optimal hand configuration (among 11) is with the hands cupped and held at an angle due to the superior low frequency spectrum. This configuration produced usable acoustic parameter measurements in the low frequency range in common room background levels unlike other configurations. The reverberation time was measured across different spaces and positions with a deviation less than three and just a noticeable difference of the signal-to-noise ratio within or near the ISO 3382-1 limits for each corresponding octave band. Other acoustic parameters (i.e., early decay time, clarity) were measured with greater deviations for reasons discussed in the text. Finally, practical steps for measurements with a handclap as an acoustic source are suggested.

Об’єктом дослідження в даній роботі є методи розрахунку акустичних параметрів конференц-залів. Метою дослідження роботи є проектування та модернізація акустичних умов конференц-залів та захист приміщень від шумів. Актуальність дослідження заключається у високому попиті на багатоцільові зали з хорошими акустичними параметри серед бізнесу та освіти. Методом дослідження є теоретичне проектування залу та покращення його акустичних параметрів за допомогою опрацювання та аналізу літури по архітектурній акустиці. Предметом дослідження є методи та засоби покращення акустичних характеристик приміщень. Практичним значенням роботи є застосування результатів аналізу в проектуванні та побудові конференц-залів з оптимальними характеристиками.
The object of research in this paper are the methods of calculating the acoustic parameters of conference rooms. The purpose of the study is to design and upgrade the acoustic conditions of conference rooms and protect the premises from noise. The relevance of the study lies in the high demand for multi-purpose halls with good acoustic parameters among business and education. The research method is the theoretical design of the hall and the improvement of its acoustic parameters through the processing and analysis of literature on architectural acoustics. The subject of research is methods and means of improving the acoustic characteristics of the premises. The practical significance of the work is the application of the results of the analysis in the design and construction of conference rooms with optimal characteristics.

Les Noyaux actifs de galaxie (AGN) incluent les sources quasi stables les plus énergétiques connues dans l'univers jusqu'à aujourd’hui. Du fait de leur distance, de leur haute luminosité et de leur petite taille, leurs régions intérieures ne sont pas directement résolvables avec les télescopes actuels. C’est pour ces raisons que nous avons besoin de techniques d’observation indirectes et de modèles théoriques pour discerner leur structure. Dans cette optique, le rôle de la polarimétrie est crucial. Elle a été ces dernières années la méthode clé qui a permis de développer le modèle unifié des AGN et pourrait, à l’avenir, nous offrir des nouveaux éléments pour sonder les régions des AGN irrésolues. Dans cette thèse, j’ai conduit des simulations sur les transferts radiatifs relatifs aux rayonnements continus émis des différentes régions intérieures des AGN en utilisant la nouvelle technique de cartographie de réverbération polarimétrique. Ce travail a été inspiré par les recherches de Gaskell et al. (2012). Le but de cette recherche est de fournir des modèles théoriques sur les différents composants des AGN en considérant le rayonnement polarisé en fonction du temps. La polarisation induite par la diffusion a été modélisée et différentes géométries de poussières circumnucléaires ont été testées. Les résultats incluent les effets de l’agrégation des poussières et différentes compositions de poussière. Pour étendre le modèle, les effets complémentaires des vents ionisés s’étirant en direction des pôles ont également été étudiés ainsi que ceux de l’anneau de diffusion équatorial théorique, avec pour postulat qu'il explique l’angle de polarisation observé dans les pôles des AGN. Les simulations ont été exécutées en utilisant une version du code STOKES incluant la dépendance temporelle. Il sera possible d'étendre ce travail à l'avenir. Les prochaines étapes suggérées incluront des raies d'émission aux modélisations ainsi que plus de complexité concernant la géométrie et la distribution de la poussière et/ou des électrons dans les régions de diffusion. Ce travail sera important pour profiter de futures données observationnelles systématiques avec un bon échantillonnage temporel
Active galactic nuclei (AGN) include the most powerful quasi-steady sources of energy known to date in the universe. Due to their distance, high brightness and small size, their inner regions are not directly resolvable with current telescopes. This is the reason why indirect techniques and theoretical models are needed to discern their structure. In this scenario the role of polarimetry is crucial. In the past it was the key method that led to the development of the Unified Model of AGN and in the future, it may give us new clues to probe unresolved AGN regions. In this thesis, I conducted radiative transfer simulations for continuous radiation of different inner regions of the AGN using the new technique of polarimetric reverberation mapping. This work has been inspired by the work of Gaskell et al. (2012). The goal of this research is to provide theoretical models of the different components of the AGN considering time-dependent polarized radiation. Scattering induced polarization has been modeled and different circumnuclear dust geometries have been explored. The results include the effects of clumpiness and different dust compositions. To further extend the model, the effects of additional extended ionized winds along the polar direction have also been explored as well as the putative equatorial scattering ring postulated to explain the polarization angle observed in pole-on AGN. The simulations were run using a time-dependent version of the STOKES code. It will be possible to extend this work in the future. Suggested future steps are including emission lines in the models, as well as more complexity in the geometry and distribution of dust and/or electrons in the scattering regions. This work will be important for taking advantage of systematic future observational data with good temporal sampling

碩士
國立中興大學
環境工程學系所
100
Nowadays people participates more indoor recreational and cultural activities such as Movies, Concert, Theater and Orchestra. Therefore, levels of comfort of ‘acoustic environment’ gradually attract more intensions. This study employed genetic algorithm and Eyring equation to investigate the optimal design of ‘reverberation time (RT)’ for theater’s acoustic environment. Two different scenarios were evaluated to investigate the sound-absorbing material costs for designing theaters to meet the ideal or recommended RT. The first scenario considers the best theater designs whose RTs are closest to the ideal values. The results show that all designed RT are ±2% deviated from the ideal RT values. The second scenario considers the lowest-cost theater designs whose RTs meet the required value intervals. The results indicate that all design RT fall in the intervals recommended by Knudsen except case III. The RT values in the 125, 250, 500, 1000 and 2000Hz octave band calculated in this study are similar to those simulated by ODEON room acoustics software. However, RT values of 4000Hz are overestimated than ODEON.

Abstract An 1,100 km2 400-fold seismic survey was acquired over some of the largest sand dunes in UAE in 2007. Large sand dunes generate many challenges for seismic processing due to the irregular data acquisition, large statics caused by the significant difference between the sand and sabkha velocities, and a massive amount of reverberation noise that hides the signal in the data. Occidental and ADNOC Sour Gas reprocessed this survey from January 2019 to August 2020 to overcome the challenges of the strong sand dune noise. For the first time, it was processed through prestack depth migration (PSDM). The primary objectives of the reprocessing project were to get an accurate PSDM volume that tied all of the available well control data; and to derive as accurate seismic amplitudes as possible over the target reservoir interval from near to far offsets to enable elastic inversion for reservoir porosity and net-thickness prediction. Whilst the reprocessing project achieved the project objectives and generated good subsurface images, it did not run as smoothly as hoped, despite being processed by one of the premier multinational processing companies. The extremely large sand dunes, which are present across most of the survey area, created major imaging problems. Key technical lessons learnt during reprocessing included: (1) CRS errors occurred sporadically during acquisition, requiring correction; (2) the sand curve (Liner, 2008) worked well for sand dune static corrections for this data set; (3) near surface statics changed whilst the survey was acquired by up to 6 ms - each shot station needed to be corrected for these statics changes because the shot stations were acquired twice with a symmetric split recording spread; and (4) the contractor's standard post-migration processing sequence (gather flattening, radon, noise attenuation, stack) did not work well for this very noisy data set. Next time we work with similar data and require a high quality result, we know to double the estimated project timeline as every step in the processing sequence takes much longer than expected when the signal-to-noise ratio of the data is very low. The novelty of this work was that we obtained large improvements in the seismic stack by applying offline gather conditioning before calculating trim statics to optimally flatten the very noisy migrated offset vector tile (OVT) gathers, prior to running the final noise attenuation and stacking workflows. Without this offline gather conditioning, the trim statics workflow mostly aligned the noise and damaged the stack.