In many real-world situations, speech signals are degraded by the reverberant effects of the environment in which they are produced. Traditional speech processing problems are typically much more difficult to solve in a reverberant setting. My research, under the guidance of Prof. Michael Brandstein, addresses a variety of traditional speech processing problems where robust solutions for reverberant environments were lacking. In general, the approaches taken in this research involve the analysis of speech data acquired at multiple, spatially diverse microphones. In the following publications, multi-channel techniques are presented for speech dereverberation, time delay estimation, pitch estimation, and source localization.
	Griebel, S., "A Microphone Array System for Speech Source Localization, Denoising, and Dereverberation," Ph.D. Thesis, Harvard University, 2002. [download PDF]
	Audio Samples: Denoising Example: A real room recording with 3 parts: a single-microphone noisy recording, the delay-and-sum beamformed result of 16 microphones, and the result of the proposed MCMSD algorithm. See the thesis for the room setup. Fan noise was at 70 dB. Dereverebration Example: A simulated room recording with 4 parts: the original clean speech utterance, the single-microphone result, the delay-and-sum beamformed result of 16 microphones, and the result of the proposed MCMBD algorithm. See the thesis for the room setup. The room had a 400 msec reverberation time. Simultaneous Denoising and Dereverberation Example: A simulated room recording with 4 parts: the original clean speech utterance, the single-microphone result, the delay-and-sum beamformed result of 16 microphones, and the result of the proposed MCMBD algorithm. See the thesis for the room setup. The room had a 400 msec reverberation time.
	Griebel, S. and Brandstein, M., "Microphone Array Source Localization Using Realizable Delay Vectors," IEEE Workshop on Applications of Signal Processing To Audio and Acoustics, New Paltz, NY, October, 2001. [download PDF]
	Griebel, S. and Brandstein, M., "Microphone Array Speech Enhancement Using Coarse Channel Modeling," International Conference of Acoustics, Speech, and Signal Processing, Salt Lake City, Utah, May, 2001. [download PDF]
	Brandstein, M. and Griebel, S., "Explicit Speech Modeling for Microphone Array Applications," Microphone Arrays: Techniques and Applications, Springer-Verlag, Heidelberg, 2001. [download PDF]
	Wang, C., Griebel, S., and Brandstein, M., "Robust Automatic Video-Conferencing with Multiple Cameras and Microphones," Proceedings of the IEEE International Conference on Multimedia and Exposition, New York, NY, July 2000. [download PDF]
	Brandstein, M. and Griebel, S., "Nonlinear, Model-Based Microphone Array Speech Enhancement," Acoustic Signal Processing For Telecommunication, Kluwer Academic Publishers, Boston, MA, 2000. [download PDF]
	Griebel, S. and Brandstein, M., "Wavelet Transform Extrema Clustering for Multi- Channel Speech Dereverberation," Proceedings of the International Workshop on Acoustic Echo and Noise Control, Pocono Manor, PA, September, 1999. [download PDF]
	Griebel, S., "Multi-Channel Wavelet Techniques for Reverberant Speech Analysis and Enhancement," Harvard Intelligent Multi-Media Environment Laboratory Technical Report, February 1999. [download PDF]