This diploma thesis deals with impact of room acoustics on automatic speech recognition (ASR) accuracy. Experiments were evaluated on speech corpus LibriSpeech and database of impulse responses and noise called ReverbDB. Used ASRs were based on Mini LibriSpeech recipe for Kaldi. First it was examined how well can ASR learn to transcribe in selected environments by using the same acoustic conditions during training and testing. Next, experiments were carried out with modifications of ASR architecture in order to achieve better robustness against new conditions by using methods for adapation to room acoustics - r-vectors and i-vectors. It was shown that recently proposed method of r-vectors is beneficial even when using real impulse responses for data augmentation.

Response reconstruction is used to obtain accurate replication of vehicle structural responses of field recorded measurements in a laboratory environment, a crucial step in the process of Accelerated Destructive Testing (ADT). Response Reconstruction is cast as an inverse problem whereby the desired input is inferred using the measured outputs of a system. ADT typically involves large shock loadings resulting in a nonlinear response of the structure. A promising linear regression technique known as Spanning Basis Transformation Regression (SBTR) in con- junction with non-overlapping windows casts the low dimensional nonlinear problem as a high dimensional linear problem. However, it is determined that the original implementation of SBTR struggles to invert a broader class of sensor configurations. A new windowing method called AntiDiagonal Averaging (ADA) is developed to overcome the shortcomings of the SBTR im- plementation. ADA introduces overlaps within the predicted time signal windows and averages them. The newly proposed method is tested on a numerical quarter car model and is shown to successfully invert a broader range of sensor configurations as well as being capable of describing nonlinearities in the system. / Dissertation (MEng)--University of Pretoria, 2021. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Att konstruktioner som innehållande roterande element riskerar att utsättas för resonans är något en konstruktör alltid bör ha i åtanke. Alla konstruktioner har naturliga frekvenser även kallat egenfrekvenser, naturliga rörelsemönster, vars frekvens beror på dess massa och styvhet. Resonans uppstår då dessa naturliga frekvenser ligger nära angripande krafters frekvens. Resonansfenomenet amplifierar den dynamiska lasten och ofta uppstår väldigt höga påfrestningar på konstruktionen. Denna rapport redogör för en vibrationsanalys av en fläktkonstruktion, samt ett utvecklingsarbete för att optimera denna fläkt utifrån uppsatta krav från samarbetspartnern Quant Service Sweden AB. Fläktkonstruktionen finns hos kabeltillvärkaren NKT i Karlskrona. Arbetet har utförts tillsammans med Quant Service, ansvariga för underhållet på NKT. Fläktkonstruktionen har under flera tillfällen havererat genom att motorfästets skruvförband har gett vika efter allt för stora påfrestningar. Mycket tyder på att konstruktionen utsätts för stora vibrationer, där man tror att orsaken är resonans. Detta eftersom roterande delar enligt leverantör och egna tester ska vara balanserade inom givna gränsvärden. Samarbetspartnern Quant vill nu ha en redogörelse för om de höga vibrationerna orsakas av resonans eller inte, samt hur problemet kan lösas på bästa sätt. Arbetet innehåller två olika experiment, ett impulstest med impulshammare och ett test där fläktens motor startas och körs under två minuter. Konstruktionens respons har mätts med en accelerometer och den erhållna datan har använts för att beräkna en frekvensresponsfunktion, samt ett Power Spectra Density (PSD) i Matlab. Syftet med dessa experiment var att kartlägga konstruktionens egenfrekvenser och dynamiska laster för att se om dessa ligger nära varandra, och på så vis bekräfta att resonansfenomenet orsakat de kraftiga vibrationerna. Det experimentella resultatet visar på att konstruktionen har en dynamisk last på 48,3 Hz vilket motsvarar motorns varvtal på 2900 rpm. Denna dynamiska last ligger väldigt nära en utav konstruktionens egenfrekvenser, 45 Hz, vilket stärker hypotesen om resonans. De experimentella resultaten har validerats med hjälp av en modalanalys gjord i FEM-programmet Simulation Mechanical. Det experimentella impulstestet har också simulerats i programmet. Arbetet innehåller även utveckling av tre olika typer av förstärkning av fläktkonstruktionen. Syftet var att förstärka konstruktionen för att höja dess naturliga frekvenser och på så vis undvika resonansfenomenet. De tre konstruktionerna är rankade utifrån uppsatta krav med hjälp av en konceptbedömningsmatris enligt modellen concept scooring. Modalanalyser i FEM-programmet har gjorts för samtliga tre konstruktioner för att undersöka dess egenfrekvenser. Samtliga tre konstruktioner har inga egenfrekvenser under 100 Hz. Efter arbetet har Quant möjligheten att välja en utav de tre konstruktionerna för vidare implementering. / A designer must have in mind that constructions containing rotating elements risks being subjected to resonance. All constructions have got natural frequencies, also called eigenfrequencies, natural motions, where the frequency depends on its mass and stiffness. This report describes a work consisting a vibrational analysis of a fan construction. The fan construction is located at the cable manufacture NKT in Karlskrona. The work has been performed together with Quant Service, a company responsible for the maintenance at NKT. The fan construction struggle with recurrent breakdowns where the screw joints for the engine attachment were broken after large vibrations. The problem seems to occur due to the resonance phenomena, this because the rotating elements are balanced within limits according to the supplier of the fan wheels and own test performed by Quant themselves. The partner Quant service want to know if the large vibrations occurs due to resonance. The work contains two different experiments, one impulse test with an impulse hammer, and one experiment where the fan’s engine was running and driven for 2 minutes. The construction response was sampled with an accelerometer and the obtained data was used to calculate a frequency response function, and a power spectra density (PSD) in Matlab. The aim of these experiments were to obtain a survey of the constructions natural frequencies and dynamic force to analyse if they are close to each other, and by that confirm that resonance is the causing factor. The experimental result show that the construction has got a dynamic force acting with 48,3 Hz, which corresponds to the engine speed at 2900 rpm. This dynamic force is very close to one of the constructions natural frequencies at 45 Hz. This supports the hypothesis that the problems occur due to resonance. The experimental results have been validated with a modal analysis in the FEM program Simulation Mechanical. The experimental impulse test has been simulated in the program as well. The work also consists a development of three different types of strengthening of the fan construction. The aim is to increase the natural frequencies and by that avoid the resonance phenomena. The three constructions are ranked based on the requirements set by using a concept scooring matrix. Modal analysis for each of the three new constructions were created to confirmed the increased natural frequencies. The constructions all seems to have the first natural frequencies over 100 Hz. When the work was finished Quant had the possibility to pick one of the new constructions for further implementation.

The diploma thesis investigates the effect of oil price fluctuations on selected macroeconomic indicators for a set of four oil-producing countries. It provides a general overview of the development in oil prices as well as the oil production and presents a more thorough analysis of the oil production, consumption and trade in the selected countries. It utilizes the methods of Vector Autoregression, Granger causality and Impulse response via the econometric software Gretl in the analysis of the effects and compares the current literature with quantitative results.

京都大学 / 0048 / 新制・課程博士 / 博士(情報学) / 甲第21214号 / 情博第667号 / 新制||情||115(附属図書館) / 京都大学大学院情報学研究科システム科学専攻 / (主査)教授 杉江 俊治, 教授 太田 快人, 教授 大塚 敏之 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DGAM

In the aspect of electric-ship grounding, the time-domain behavior of the ship hull is needed. The grounding scheme impacts the nature of voltage transients during switching events and faults, identifiability and locatability of ground faults, fault current levels, and power quality. Due to the large size of ships compared with the wavelengths of the desired signals, time-domain measurement or simulation is a time-consuming process. Therefore, it is preferred that the behavior be studied in the frequency-domain. In the frequency-domain one can break down the whole ship hull into small blocks and find the frequency behavior of each block (scattering parameters) in a short time and then connect these blocks and find the whole ship hull scattering parameters. Then these scattering pa- rameters should be transferred to the time-domain. The problem with this process is that the measured frequency-domain data (or the simulated data) is band-limited so, while calculating time-domain solutions, due to missing DC and low frequency content the time-domain response encounters causality, passivity and time-delay problems. Despite availability of several software and simulation packets that convert frequency-domain information to time-domain, all are known to suffer from the above mentioned problems. This dissertation provides a solution for computing the Time-Domain Impulse-Response for a system by using its measured or simulated scattering parameters. In this regard, a novel wavelet computational approach is introduced.

This essay aims to ascertain whether an impulse response is able to accurately simulatethe sound of an amplifier with a clean tone. This is done with a visual analysis of thewaveforms from both a re-amped audio signal and one with a convolution reverb/loaderwith an impulse measurement of the amplifier. And an audio evaluation with musicallyknowledgeable individuals. The results show small visual differences on the waveformsand no participant in the audio evaluation test was able to tell which was an impulseresponse. Leading to the conclusion that an impulse response could simulate theamplifier with great accuracy.

In order to preserve the acoustics of the Salt Lake Tabernacle after the seismic renovation of 2005-2006, it was necessary to characterize these acoustics immediately preceding the renovation. This thesis discusses the characterization process that began with the measurement of hundreds of impulse responses for five different source positions and several receiver locations throughout the hall seating areas. The acoustics were further characterized by deriving various parameters from these responses that correlate with subjective preferences for music and speech. Impulse responses were also generated by a CATT-Acoustic™ computer model of the Tabernacle for the same purpose. The parameter values were then mapped over diagrams of the seating areas of the hall to show the spatial variation of the acoustics. To further investigate the variation, statistics were calculated for each parameter and an algorithm was developed to determine the minimum number of receiver locations necessary to adequately characterize the hall. Computer models were also used to investigate focusing effects of the curved ceiling and historical comments made about the improvements to the acoustics with addition of the balcony in 1870.

In room acoustics, the directional information of sound arrivals at a listening location can be used to diagnose the origins of problematic reflections so offending surfaces or other features can be properly treated. It can also be used for other purposes, including the study of psychoacoustic indicators. Many methods have been developed in the past to derive directional information, but despite their benefits, each has had significant drawbacks that have necessitated further research into their properties and development of an improved method. This thesis presents a review of past methods, their benefits and shortcomings. It discusses many theoretical and practical issues pertaining to the Polar ETC method and methods using the cross-correlation function. It also presents a new short-time correlation-based method (STCM) for gathering directional information of sound arrivals in rooms. Computer programs were developed for the implementation of the theory. Numerical simulations and experimental measurements are shown and the results are compared to those obtained by the Polar Energy Time Curve (ETC) method. The STCM is shown to be an improvement over past methods in terms of its ability to distinguish between simultaneous arrivals, its accuracy, its computational efficiency and its equipment requirements. Limitations of the method are also discussed.

Over the years, the Internet has become increasingly popular and people's dependence on it has increased dramatically. Whether it be to communicate to someone across the world, find blueprints, or check sports scores, the Internet has become a necessary resource for everyone. In emergency situations, this need increases further. After the terrorist attacks on the Pentagon, it took several days to restore communications. This is not an acceptable time frame when people's lives are at stake. Virginia Tech's Center for Wireless Telecommunication has developed a prototype of a rapidly deployable high bandwidth wireless communication system at 28 GHz (Local Multipoint Distribution Service frequency). This system provides a large bandwidth radio link to a disaster zone up to 5 km away and puts Ethernet speeds and 802.11 accesses to users within hours. Because of the possible variability in locations that the system can be deployed, it is necessary to find the most useable channel at the site as quickly as possible. In addition to 28GHz radio links, the system also has a built-in channel sounder that measures and captures the channel impulse response of the current channel. Until now, there has been limited research on the relationship between the channel impulse response and the usability of the channel quantified using bit error rate. This thesis examines several different channels captured by CWT's channel sounder and simulates the BER using Cadence's SPW with time-domain models of the channels. This thesis goes on further to show that BER greatly depends on the channel impulse response and the symbol rate. / Master of Science