Abstract: A system and apparatus are disclosed for identifying polysemous terms and for measuring their degree of polysemy. A polysemy index provides a quantitative measure of how polysemous a word is. A list of words can be ranked by their polysemy indices, with the most polysemous words appearing at the top of the list. A polysemy evaluation process collects a set of terms near a target term. Inter-term distances of the set of terms occurring near the target term are computed and the multi-dimensional distance space is reduced to two dimensions. The two dimensional representation is converted into radial coordinates. Isotonic/antitonic regression techniques are used to compute the degree to which the distribution deviates from unimodality. The amount of deviation is the polysemy index. A corpus can be preprocessed using the polysemy indices to identify words having clearly separated senses, allowing an information retrieval system to return a separate list of documents for each sense of a word.

Abstract: A system and method are described for determining a near-optimum subset of data, based on a selected model, from a large corpus of data. Sets of feature vectors corresponding to natural or other preselected divisions of the data corpus are mapped into matrices representative of such divisions. The invention operates to find a submatrix of full rank formed as a union of one or more of those division-based matrices. A greedy algorithm utilizing Gram-Schmidt orthonormalization operates on the division matrices to find a near optimum submatrix and in a time bound representing a substantial improvement over prior-art methods. An important application of the invention is the selection of a small number of sentences from a corpus of a very large number of such sentences from which the parameters of a duration model for speech synthesis can be estimated.

Abstract: A system and method are provided for automatically computing local pitch contours from textual input to produce pitch contours that closely mimic those found in natural speech. The methodology of the invention incorporates parameterized equations whose parameters can be estimated directly from natural speech recordings. That methodology incorporates a model based on the premise that pitch contours instantiating a particular pitch contour class can be described as distortions in the temporal and frequency domains of a single, underlying contour. After the nature of the pitch contour for different pitch contour classes has been established, a pitch contour can be predicted that closely models a natural speech contour for a synthetic speech utterance by adding the individual contours of the different intonational classes and adjusting the boundaries of these to match the boundaries of the adjacent intonation curves.

Abstract: A speech synthesis method employs an acoustic element database that is established from phonetic sequences occurring in an interval of a speech signal. In establishing the database, trajectories are determined for each of the phonetic sequences containing a phonetic segment that corresponds to a particular phoneme. A tolerance region is then identified based on a concentration of trajectories that correspond to different phoneme sequences. The acoustic elements for the database are formed from portions of the phonetic sequences by identifying cut points in the phonetic sequences which correspond to time points along the respective trajectories proximate the tolerance region. In this manner, it is possible to concatenate the acoustic elements having a common junction phonemes such that perceptible discontinuities at the junction phonemes are minimized. Computationally simple and fast methods for determining the tolerance region are also disclosed.