In this paper we describe the development of rules to drive a quasi-articulatory speech synthesizer, HLsyn. HLsyn has 13 parameters, which are mapped to the parameters of a formant synthesizer. Its small number of parameters combined with the computational simplicity of a formant synthesizer make it a good basis for a text-to-speech system. An overview of the rule-driven system, called VHLsyn, is presented. The system assumes a phonetic string as input, and produces HLsyn parameter tracks as output. These parameter tracks are then used by HLsyn to produce synthesized speech. Previous work to improve the synthesis of consonants and suprasegmental effects is described, and is shown to improve the quality of the output speech. The improvements include refinement of release characteristics of stop consonants, methods for control of vocal-fold parameters for voiced and voiceless consonants, and rules for timing and intonation.

With the goal of synthesizing natural-sounding speech based on higher-level parameters, sources of vowel amplitude variation were studied for sentences having different prosodic patterns. Previous theoretical and experimental work has shown that sound pressure level (SPL) is proportional to subglottal pressure (P/sub s/) on a log scale during production of sustained vowels. The current work is based on acoustic sound pressure signals and estimated P/sub s/ signals recorded during the production of reiterant speech, which is closer to natural speech production and includes prosodic effects. The results show individual, and perhaps gender, differences in the relationship between SPL and P/sub s/, and in the degree of vowel amplitude contrast between full and reduced vowels. However, a general trend among speakers is to use subglottal pressure to control vowel amplitude at sentence level and main prominences, and to use adjustments of glottal configuration to control vowel amplitude variations for reduced and non-nuclear full vowels. These results have implications not only for articulatory speech synthesis, but also for automatic speech recognition systems.

We address the measurement of glottal characteristics of female speakers and how these characteristics contribute to voice quality or individuality. We have developed acoustic measurements of the voicing source that are made directly on the speech waveform or spectrum. These measures are based on theoretical models of speech production. Based on these measurements it is possible to make some inferences about the glottal configuration during phonation and the nature of the glottal pulse. Previous work has relied mainly on physiological methods such as inverse filtering of vocal tract airflow or observations of vocal fold vibration via endoscopy or fiberscopy. Our measures are non-invasive and can be easily extracted automatically. By comparing these acoustic measures to physiological and perceptual data, we show that they are valid.

This correspondence presents an experimental system that uses an energy-tracking operator and a related energy separation algorithm to automatically find speech formants and amplitude/frequency modulations in voiced speech segments. Initial estimates of formant center frequencies are provided by either LPC or morphological spectral peak picking. These estimates are then shown to be improved by a combination of bandpass filtering and iterative application of energy separation.>