Showing papers by "Ronald W. Schafer published in 2008"

On the quality assessment of sound signals

Abstract: This paper constitutes an introduction to the field of quality evaluation of sound (speech and audio) signals. The need for such an assessment is inherent to modern communications: VoIP, mobile phone, or teleconference systems require meaningful measures of performance, which may ultimately assure good service or profitable business. A brief survey on subjective and objective evaluation methods is provided. Recent developments as well as new topics to be investigated are also addressed. Experiments are conducted to illustrate how to validate quality assessment methods.

Reverberation Assessment in Audioband Speech Signals for Telepresence Systems.

Abstract: Modern telepresence systems constitute a new challenge for quality assessment of multimedia signals. This paper focuses on the evaluation of the reverberation impair ent for audioband speech signals. A review on the reverberation effect is presented, with emphasis given on the mathematical modeling of its components, including early reflections and late reverberation. A subje ctiv test for evaluating the human perception of the reverberation phenomenon is completely described, fro m its conception to the final results. Analyses are provided comparing the average subjective grades to curren t quality-evaluation standards for speech and audio signals. It is observed that the PESQ and PEAQ objective algo rithms constitute interesting starting points for developing an objective method for measuring the reverbera tion effect on speech signals.

Homomorphic Systems and Cepstrum Analysis of Speech

Abstract: In 1963, Bogert, Healy, and Tukey published a chapter with one of the most unusual titles to be found in the literature of science and engineering [9.1]. In this chapter, they observed that the logarithm of the power spectrum of a signal plus its echo (delayed and scaled replica) consists of the logarithm of the signal spectrum plus a periodic component due to the echo. They suggested that further spectrum analysis of the log spectrum could highlight the periodic component in the log spectrum and thus lead to a new indicator of the occurrence of an echo. Specifically they made the following observation: In general, we find ourselves operating on the frequency side in ways customary on the time side and vice versa. As an aid in formalizing this new point of view, they introduced a number of paraphrased words. For example, they defined the cepstrum of a signal as the power spectrum of the logarithm of the power spectrum of a signal. (In fact, they used discrete-time spectrum estimates based on the discrete Fourier transform.) Similarly, the term quefrency was introduced for the independent variable of the cepstrum [9.1].

Maximum Likelihood Time Delay Estimation with Phase Domain Analysis in the Generalized Cross Correlation Framework

Abstract: We propose a new method for efficiently estimating the maximum likelihood frequency weighting in the generalized cross correlation framework for time delay estimation. The estimation is based on the analysis of the cross spectrum between a pair of microphones. We model how phase distribution is affected by both noise and reverberation, and relax the common assumption that noise and reverberation are uncorrelated with the source. Thus, our method does not require knowledge of the noise spectrum or a detailed model of the reverberation. Experimental results show that the proposed method is superior to the PHAT method.

Quality Evaluation of Reverberation in Audioband Speech Signals

Abstract: Modern telepresence systems constitute a new challenge for quality assessment of multimedia signals. This paper focuses on the evaluation of the reverberation impairment for audioband speech signals. A review on the reverberation effect is presented, with emphasis given on the mathematical modeling of its components, including early reflections and late reverberation. A subjective test for evaluating the human perception of the reverberation phenomenon is completely described, from its conception to the final results. Analyses are provided comparing the average subjective grades to current quality-evaluation standards for speech and audio signals. It is verified how the reverberation perception can be mapped onto three main system characteristics: reverberation time (associated to the room acoustical properties), source-microphone distance, and room volume. Direct estimation of these parameters from the room impulse response is discussed. One established reverberation measure is then revisited in the audioband speech context, showing high correlation with the subjective grades previously obtained.

4D Segmentation of Cardiac Data Using Active Surfaces with Spatiotemporal Shape Priors.

Abstract: To the memory of my father, Youssef Abufadel To my mother, Emilie Awad Abufadel iii ACKNOWLEDGEMENTS My graduate career has been a long journey during which I have been blessed to have many great relationships. I would like to grab this opportunity to express my thanks and gratitude to those who have help me through this experience. I owe extreme gratitude to my mentor, Dr. Schafer. His continuous support gave me the strength and courage to keep going. His understanding and flexibility helped me shape my own path as graduate student. It has been both an honor and a pleasure to work with someone who is insightful, helpful, kind, thorough and patient-an outstanding advisor. I also have been fortunate to have have had the opportunity to work under the guidance of Dr. Yezzi. His profound understanding and knowledge of the different aspects of image segmentation gave me confidence and helped me understand and implement new ideas and procedures. His extremely efficient programming techniques allowed me to optimize my programs to reduce the enormous time it took to perform the many tests that were required. His understanding and support gave me the opportunity continue with my degree and I thank him for that. This research would not have been possible with out the help and support of Dr. Robert Eisner and Dr. Marijn Brummer of Emory University. They were extremely generous in extending their help and support that allowed me utilize the MRI scanners at Crawford Long Hospital and Emory University. Without their aid, I would not have been able to build the invaluable training database that was needed for this research and I am grateful for that. I thank them for the helpful discussions and valuable advice that they provided. I would also like to thank Susan Eder for helping me scan the numerous volunteers. Next, I would like to thank all faculty of the Center of Signal and Image Processing (CSIP) at Georgia Tech. They have all worked hard to push CSIP to the forefront of teaching and research in digital signal processing. I am grateful for all the professors that I have taken classes with as well as those who have opened their doors to me. I specially iv would like to thank Dr. McClellan for his insight and advice on how to test different ideas in Matlab. Over the years of my graduate studies, I have had …