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Time-Frequency Representations for Speech Signals.
MASSACHUSETTS INST OF TECH CAMBRIDGE ARTIFICIAL INTELLIGENCE LAB
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This work addresses two related questions. The first question is what joint time-frequency energy representations are most appropriate for auditory signals, in particular, for speech signals in sonorant regions. The quadratic transf for the representation 1 shift-invariance, 2 positivity, 3 superposition, 4 locality, and 5 smoothness. The second question addressed is how to obtain a rich, symbolic description of the phonetically relevant features om these time-frequency energy surfaces, the so-called schematic spectrogram Time-frequency ridges, the 2-D analog of spectral peaks, are one feature that is proposed. If non-oriented kernels are used for the energy representation, then the ridge tops can be identified with zero-crossings in the inner project of the gradient vector and the direction of greatest downward curvature. If oriented kernels are used, the method can be generalized to give better orientation selectivity e.g., intersecting ridges at the cost of poorer time-frequency locality.
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