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Reduction of Additive Noise in the Digital Processing of Speech
Avner HalevyAMSC 664
Final Presentation May 2009
Dr. Radu BalanDepartment of Mathematics
Center for Scientific Computation and Math. Modeling
1
Background and Goal
• Digital speech signals
• Clean signals are degraded by noise– From environment
– From processing (recording, transmitting, etc.)
• Speech enhancement: reduce noise without distorting original (clean) signal
Scope and Goal
• Focus on additive white Gaussian noise
• Improve quality and intelligibility
• Use short time analysis (frames)
• Explore two algorithms:– Spectral Subtraction
– Iterative Wiener Filtering
• Test objectively using TIMIT
3
Spectral Subtraction
• Estimate the magnitude of the noise spectrum when speech is absent
• Subtract the estimate from the magnitude of the spectrum of the noisy signal
• Keep the noisy phase
• Inverse Fourier to obtain enhanced signal in time domain
4
Spectral Subtraction
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Wiener Filter - Theory
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Implementation, Validation, Testing
• Both algorithms were implemented in MATLAB on a standard PC
• Implementation validated using zero noise, stability ensured using small nonzero noise
• Testing based on TIMIT
• Main objective measure used: segmental SNR
Conclusions
• Objectively, IW produced better results
• Subjectively, both methods suffer from severe artifacts (musical noise)
• Possible improvement by more sophisticated noise estimation
Bibliography
• [1] Deller, J., Hansen, J., and Proakis, J. (2000) Discrete Time Processing of Speech Signals, New York, NY: Institute of Electrical and Electronics Engineers
• [2] Quatieri, T. (2002) Discrete Time Speech Signal Processing, Upper Saddle River, NJ: Prentice Hall
• [3] Loizou, P. (2007) Speech Enhancement: Theory and Practice, Boca Raton, FL: Taylor & Francis Group
• [4] Rabiner, L., Schafer, R. (1978) Digital Processing of Speech Signals, Englewood Cliffs, NJ: Prentice Hall
• [5] Vaseghi, S. (1996) Advanced Signal Processing and Digital Noise Reduction, Stuttgart, Germany: B.G. Teubner
• [6] Lim, J. and Oppenheim, A.V. (1978) All-pole modeling of degraded speech, IEEE Trans. Acoust. Speech Signal Process., 26(3), 197-200
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