Thesis (Ph. D.)--Florida State University, 2005. / Advisor: Qing-Xiang A. Sang, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed May 11, 2006). Document formatted into pages; contains xvii, 118 pages. Includes bibliographical references.

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Chemistry. / Includes bibliographical references.

Thesis (M.A.)--Georgia State University, 2006. / Title from title screen. Andrew Altman, committee chair; Christie Hartley, Peter Lindsay, committee members. Electronic text (88 p.) : digital, PDF file. Description based on contents viewed May 2, 2007. Includes bibliographical references (p. 80-88).

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The problem of blind separation refers to recovering original signals, called source signals, from the mixed signals, called observation signals, in a reverberant environment. The mixture is a function of a sequence of original speech signals mixed in a reverberant room. The objective is to separate mixed signals to obtain the original signals without degradation and without prior information of the features of the sources. The strategy used to achieve this objective is to use multiple bands that work at a lower rate, have less computational cost and a quicker convergence than the conventional scheme. Our motivation is the competitive results of unequal-passbands scheme applications, in terms of the convergence speed. The objective of this research is to improve unequal-passbands schemes by improving the speed of convergence and reducing the computational cost. The first proposed work is a novel maximally decimated unequal-passbands scheme. This scheme uses multiple bands that make it work at a reduced sampling rate, and low computational cost. An adaptation approach is derived with an adaptation step that improved the convergence speed. The performance of the proposed scheme was measured in different ways. First, the mean square errors of various bands are measured and the results are compared to a maximally decimated equal-passbands scheme, which is currently the best performing method. The results show that the proposed scheme has a faster convergence rate than the maximally decimated equal-passbands scheme. Second, when the scheme is tested for white and coloured inputs using a low number of bands, it does not yield good results; but when the number of bands is increased, the speed of convergence is enhanced. Third, the scheme is tested for quick changes. It is shown that the performance of the proposed scheme is similar to that of the equal-passbands scheme. Fourth, the scheme is also tested in a stationary state. The experimental results confirm the theoretical work. For more challenging scenarios, an unequal-passbands scheme with over-sampled decimation is proposed; the greater number of bands, the more efficient the separation. The results are compared to the currently best performing method. Second, an experimental comparison is made between the proposed multiband scheme and the conventional scheme. The results show that the convergence speed and the signal-to-interference ratio of the proposed scheme are higher than that of the conventional scheme, and the computation cost is lower than that of the conventional scheme.

The main focus of this thesis is the enhancement of the statistical framework employed for underdetermined T-F masking blind separation of speech. While humans are capable of extracting a speech signal of interest in the presence of other interference and noise; actual speech recognition systems and hearing aids cannot match this psychoacoustic ability. They perform well in noise and reverberant free environments but suffer in realistic environments. Time-frequency masking algorithms based on computational auditory scene analysis attempt to separate multiple sound sources from only two reverberant stereo mixtures. They essentially rely on the sparsity that binaural cues exhibit in the time-frequency domain to generate masks which extract individual sources from their corresponding spectrogram points to solve the problem of underdetermined convolutive speech separation. Statistically, this can be interpreted as a classical clustering problem. Due to analytical simplicity, a finite mixture of Gaussian distributions is commonly used in T-F masking algorithms for modelling interaural cues. Such a model is however sensitive to outliers, therefore, a robust probabilistic model based on the Student's t-distribution is first proposed to improve the robustness of the statistical framework. This heavy tailed distribution, as compared to the Gaussian distribution, can potentially better capture outlier values and thereby lead to more accurate probabilistic masks for source separation. This non-Gaussian approach is applied to the state-of the-art MESSL algorithm and comparative studies are undertaken to confirm the improved separation quality. A Bayesian clustering framework that can better model uncertainties in reverberant environments is then exploited to replace the conventional expectation-maximization (EM) algorithm within a maximum likelihood estimation (MLE) framework. A variational Bayesian (VB) approach is then applied to the MESSL algorithm to cluster interaural phase differences thereby avoiding the drawbacks of MLE; specifically the probable presence of singularities and experimental results confirm an improvement in the separation performance. Finally, the joint modelling of the interaural phase and level differences and the integration of their non-Gaussian modelling within a variational Bayesian framework, is proposed. This approach combines the advantages of the robust estimation provided by the Student's t-distribution and the robust clustering inherent in the Bayesian approach. In other words, this general framework avoids the difficulties associated with MLE and makes use of the heavy tailed Student's t-distribution to improve the estimation of the soft probabilistic masks at various reverberation times particularly for sources in close proximity. Through an extensive set of simulation studies which compares the proposed approach with other T-F masking algorithms under different scenarios, a significant improvement in terms of objective and subjective performance measures is achieved.

Whether or not major changes in family structure during adolescence have positive or negative consequences for adolescents has not been empirically investigated to any extent. The separation-individuation process is considered to be facilitated when adolescents can express themselves in a family context characterized by emotional connectedness (Grotevant & Cooper, 1986). This individuation process is not concerned exclusively with separation or autonomy but rather with the continuing embeddedness of the individual in relationships with others (Karpel, 1976; Youniss, 1983). The impact of parental death on the process of separation-individuation in adolescence was examined in this study. Thirty male and female adolescents, ages 12 to 16 years, from families in which the father had died participated in this study. They were compared with thirty adolescents of comparable age from intact families. The adolescents completed instruments that provided information about development of autonomy (Emotional Autonomy Scale), attachment to mother, father and peers (Inventory of Parent and Peer Attachment), and adolescents’ perception of family functioning (Family Functioning in Adolescence Questionnaire). Adolescents from the father-deceased group are more autonomous than the intact group in some of the scales. Males from the father- deceased group scored significantly higher than males from the intact group on the emotional autonomy subscales. Adolescents in the father-deceased families showed similar attachment to fathers and mothers when compared with adolescents from intact families. Adolescents’ perceptions of their family functioning showed similar results for both the father-deceased and intact groups with adolescents who scored high in family functioning being less autonomous. Similarly adolescents from the father-deceased group who were more attached to mothers showed less autonomy according to their scores on the Emotional Autonomy Scale. Adolescents’ attachment to peers was unrelated to their level of autonomy. / Graduate

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