Mats Ljungqvist

Proposal and evaluation of models for the glottal source waveform

Speech analysis for high quality speech synthesis or high accuracy speech recognition requires realistic models not only for the vocal tract but also for the voice source. In the present paper, we investigate models for the glottal volume velocity waveform. Previously proposed models are reviewed and classified according to their level of elaboration in expressing the glottal characteristics. A new model is then proposed which possesses all the important features of previously proposed models. A method is also described for simultaneously estimating the glottal source and vocal: tract parameters. Using this method, evaluation of glottal model parameters is carried out on real speech by varying the number of parameters in the proposed model. The results indicate the importance of detailed modeling of the period of glottal closure for accurate analysis.

Estimation of voice source and vocal tract parameters based on ARMA analysis and a model for the Glottal source waveform

Conventional speech analysis methods based on linear prediction often fail to separate and estimate the source and vocal-tract characteristics, especially in the case of voiced sounds, because of oversimplified assumptions regarding the voice source. We have already proposed a model that is capable of expressing a wide range of voice source characteristics, and demonstrated that source and vocal-tract parameters can be well separated and correctly estimated, for vowel and vowel-like sounds, by combining the proposed source model with the linear predictive analysis. The present paper extends our approach to apply to a wider variety of speech sounds including nasal vowels and nasal consonants, by combining the proposed source model with the ARMA analysis. The validity of the system was demonstrated by analysis of synthetic and natural speech.

Analysis and modeling of word accent and sentence intonation in Swedish

In Swedish, the fundamental frequency contour (F/sub 0/ contour) is known to be the main acoustic feature for word accent and sentence intonation. The authors propose a model for the generation process of F/sub 0/ contours of Swedish, based on an extension of the model for Japanese. As the input to this model, two kinds of command are assumed: phrase commands, which are always positive impulses, and accent commands, which are stepwise functions of both polarities. Analysis-by-synthesis of F/sub 0/ contours of both isolated words and sentences, uttered by two native speakers from the Stockholm region, indicated that the model can always generate very close approximations to observed F/sub 0/ contours, and that the extracted parameters are systematically related to the underlying lexical word accent, syntactic structure, and focus. This demonstrates the basic validity of the model and its utility in speech synthesis.<<ETX>>

Prosody generation in text-to-speech conversion using dependency graphs

Addresses the problem of prosody assignment in the context of a system for text-to-speech conversion of Swedish. The question of what type of textual analysis is needed for prosodic purposes is discussed and the use of dependency graphs to this end is proposed. It is argued that this type of analysis provides sufficient syntactic information so that prosodic phrasing and prominence assignment algorithms can be successfully applied. The ability of the system to generate acceptable prosodic descriptions is evaluated by comparison with examples of prosodically analysed naturally spoken sentences.