Detection and identification of occluders using the wavelet transform.

Summary The work presented in this thesis is part of the acoustic-phonetic decoding of speech. In this context, two steps have been dissociated: the detection and the recognition of French occluders using the wavelet transform. In the detection stage, we tried to approximate the bar of explosion of the occluders by an impulse. The validation of this model is done by analyzing the correlation functions between the modulus of the wavelet transform of the speech signal and that of the analyzing wavelet. For deaf occluders (respectively sonorous), a detection rate equal to 89.5% (respectively 67.6%) is associated with a false alarm rate of 10.5% (respectively 32.4%). The interest of our detection system is twofold. On the one hand, it allows the localization of the explosion bar with an error of between 0.2 ms and 1 ms depending on the frequency structure of the occlusion. On the other hand, it allows to measure the more or less impulsive character of the occlusive. Although robust, the detection system is less efficient for noisy signals. A prior reduction of the background noise level does not systematically improve the detection rates. Using blast bar detection, the recognition system is based on the statistical analysis of the average of the wavelet coefficients over a time support equal to one millisecond. Three analyses have been evaluated: discriminant analysis, segmentation trees and maximum likelihood trees. The discriminant analysis is characterized by an identification rate higher than 74% for contextual recognition. Moreover, it allows to recognize 70% of the false detections of the detection module. Due to the evaluation and performance of each of these methods, only the recognition rates of this analysis are compared to those of ten systems described in the literature. For a 99% confidence interval, seven of them show non-significantly different performance. This comparison shows that the high frequency smoothing of the wavelet transform is not a major handicap for the recognition of deaf occluders as one might have supposed.