Room acoustic modeling

Tato práce se zabývá geometrickými modelovacími metodami a jejich implementací v~prostředí Octave (Matlab), které je pro praktickou realizaci ideální. V první části je práce zaměřena na velmi zjednodušenou metodu zrcadlových zdrojů, která je schopna vypočítat a vykreslit impulzní odezvu pravoúhlých 2D místností. V další části je věnována pozornost metodě stejné, avšak rozšířené o možnost simulace trojrozměrných místností ve tvaru mnohostěnných hranolů. Nejdřívě je vysvětlena z hlediska teoretického a matematického, následně je i podrobně zdokumentována její implementace. Metoda rozšířená dokáže kromě grafického znázornění impulzní charakteristiky také vygenerovat její zvukovou reprezentaci a následně ji využít pro auralizaci, které je dosaženo za pomoci konvoluce definovaného vstupního zvuku s výslednou impulzní odezvou. K oběma metodám je uveden příklad použítí včetně vysvětlujících obrazových znázornění.This Master's Thesis deals with geometric modeling methods and theirs implementation in Octave (Matlab), which is ideal for the practical realization. The first part of the thesis is focused on a very simplified image source method, which is able to calculate and render the 2D impulse response of rectangular rooms. The next part is aimed on~the same method, but extended by three-dimensional simulation of polyhedral prism-shaped rooms. There is both an explanation of theoretical and mathematical aspects and a~documentation of the implemented source code. Extended image source method is able to generate sound representation of impulse response characteristics, and use it for auralization, which is achieved by using convolution of both the input sound source and the calculated impulse response. At the end there are two practical examples for both methods with explanatory illustrations.

Structured Sparsity Models for Multiparty Speech Recovery from Reverberant Recordings

We tackle the multi-party speech recovery problem through modeling the acoustic of the reverberant chambers. Our approach exploits structured sparsity models to perform room modeling and speech recovery. We propose a scheme for characterizing the room acoustic from the unknown competing speech sources relying on localization of the early images of the speakers by sparse approximation of the spatial spectra of the virtual sources in a free-space model. The images are then clustered exploiting the low-rank structure of the spectro-temporal components belonging to each source. This enables us to identify the early support of the room impulse response function and its unique map to the room geometry. To further tackle the ambiguity of the reflection ratios, we propose a novel formulation of the reverberation model and estimate the absorption coefficients through a convex optimization exploiting joint sparsity model formulated upon spatio-spectral sparsity of concurrent speech representation. The acoustic parameters are then incorporated for separating individual speech signals through either structured sparse recovery or inverse filtering the acoustic channels. The experiments conducted on real data recordings demonstrate the effectiveness of the proposed approach for multi-party speech recovery and recognition.Comment: 31 page

A round robin on room acoustical simulation and auralization

A round robin was conducted to evaluate the state of the art of room acoustic modeling software both in the physical and perceptual realms. The test was based on six acoustic scenes highlighting specific acoustic phenomena and for three complex, “real-world” spatial environments. The results demonstrate that most present simulation algorithms generate obvious model errors once the assumptions of geometrical acoustics are no longer met. As a consequence, they are neither able to provide a reliable pattern of early reflections nor do they provide a reliable prediction of room acoustic parameters outside a medium frequency range. In the perceptual domain, the algorithms under test could generate mostly plausible but not authentic auralizations, i.e., the difference between simulated and measured impulse responses of the same scene was always clearly audible. Most relevant for this perceptual difference are deviations in tone color and source position between measurement and simulation, which to a large extent can be traced back to the simplified use of random incidence absorption and scattering coefficients and shortcomings in the simulation of early reflections due to the missing or insufficient modeling of diffraction.DFG, 174776315, FOR 1557: Simulation and Evaluation of Acoustical Environments (SEACEN

Investigating the stability of frequency-dependent locally reacting surface boundary conditions in numerical acoustic models

Numerical acoustic modeling enables simulation of sound propagation through bounded space. Recent research directed to refining Finite Difference Time Domain solutions for acoustic prediction has focused on emulating sound wave-surface interaction. Locally reacting surface properties are a popular choice for deriving boundary conditions that incorporate surface absorption properties. However, implementation of these boundary conditions, using the methods described in prevalent literature, is demonstrated here as unstable for complex room geometries. This work presents a reformulated implementation of frequency-dependent locally reacting surface boundary conditions for Finite Difference Time Domain simulations that is empirically demonstrated to be robust against simulation instabilities

A Comparison of Acoustical Performance Between Traditional and Modern Church

Due to various worship approaches, churches' plans and designs have evolved over time. In traditional churches, the chancel is where the preacher and choir are while the nave is where the audience is seated. The modern churches on the other hand usually follow the auditorium layout, where the chancel is replaced by a stage. The stage serves as a space for the musical worship and performances, other than preaching by the pastors. In acoustical terms, the chancel and the stage are known as the sound source and the audience is the sound receiver. It is essential to understand the relationship between the differences in the characteristics of traditional and modern churches and the impact on their acoustical performance. Two churches with different layout (cruciform and rectangular) from traditional and modern churches in Malaysia were selected to run a computer simulation using ODEON Room Acoustic Software. The results were then reviewed and analysed in acoustical parameters: (i) Reverberation Time (RT) and (ii) Speech Transmission Index (STI).  Smaller church scored better in STI thus it is better for speech driven worship service as while bigger church scored better in RT thus it is more ideal for musical worship. In addition, the existing materials found in modern churches improved the overall acoustical performances. In conclusion, the church acoustical performance is affected by factors like the volume, distance between the sound origin, receivers and the surrounding walls, total absorption area and types of surface material and its absorption coefficient

A Comparison of Acoustical Performance Between Traditional and Modern Church

Due to various worship approaches, churches' plans and designs have evolved over time. In traditional churches, the chancel is where the preacher and choir are while the nave is where the audience is seated. The modern churches on the other hand usually follow the auditorium layout, where the chancel is replaced by a stage. The stage serves as a space for the musical worship and performances, other than preaching by the pastors. In acoustical terms, the chancel and the stage are known as the sound source and the audience is the sound receiver. It is essential to understand the relationship between the differences in the characteristics of traditional and modern churches and the impact on their acoustical performance. Two churches with different layout (cruciform and rectangular) from traditional and modern churches in Malaysia were selected to run a computer simulation using ODEON Room Acoustic Software. The results were then reviewed and analysed in acoustical parameters: (i) Reverberation Time (RT) and (ii) Speech Transmission Index (STI).  Smaller church scored better in STI thus it is better for speech driven worship service as while bigger church scored better in RT thus it is more ideal for musical worship. In addition, the existing materials found in modern churches improved the overall acoustical performances. In conclusion, the church acoustical performance is affected by factors like the volume, distance between the sound origin, receivers and the surrounding walls, total absorption area and types of surface material and its absorption coefficient