Helen M. Hanson

Towards models of phonation

Abstract The earliest models of phonation were based on the assumption that the glottis is closed during a part of the vibration cycle, that is, the phonation is modal. Nonmodal phonation, however, commonly occurs not only for disordered voice but also for normal voices, which often exhibit a breathy quality or irregular vibration. In this paper, we review recent work that examines acoustic data and models of nonmodal phonation in both normal and disordered voice. We first describe acoustic models that predict how the glottal source varies from modal phonation to phonation resulting from glottal configurations that are partially abducted, including a posterior glottal opening. These models are applied first to vowels of nondisordered adults, and, later in the paper, to vowels produced by adults with dysarthria. We also present results from a study in which a modified version of the two-mass model is used to resolve a seeming conflict among aerodynamic and acoustic data collected from adult female subjects with vocal-fold nodules. Some discussion of nonmodal phenomena that occur due to prosodic and emotional influences is included. Overall, it appears that current models of modal phonation can be extended to include a range of nonmodal phonation types.

A quasiarticulatory approach to controlling acoustic source parameters in a Klatt-type formant synthesizer using HLsyn

The HLsyn speech synthesizer uses models of the vocal tract to map higher-level quasiarticulatory parameters to the acoustic parameters of a Klatt-type formant synthesizer. The benefits of this system are several. In addition to requiring a relatively small number of parameters, the HLsyn model includes constraints on source-filter relations that occur naturally during speech production. Such constraints help to prevent combinations of sources and filter that are impossible to achieve with the human vocal tract. Thus, HLsyn could lead to reductions in the complexity of formant synthesis and result in better quality synthesis. HLsyn can also be a useful tool for speech-science education and speech research. This paper focuses on the generation of acoustic sources in HLsyn. Described in detail are the equations and methods used to estimate Klatt-type source parameters from HLsyn parameters. Several examples illustrating the generation of source parameters for obstruents (voiced and voiceless) and sonorants are provided. Future papers will describe the filtering components of HLsyn.

A system for finding speech formants and modulations via energy separation

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. >

Effects of obstruent consonants on fundamental frequency at vowel onset in English

When a vowel follows an obstruent, the fundamental frequency in the first few tens of milliseconds of the vowel is known to be influenced by the voicing characteristics of the consonant. This influence was re-examined in the study reported here. Stops, fricatives, and the nasal /m/ were paired with the vowels /i,a/ to form CVm syllables. Target syllables were embedded in carrier sentences, and intonation was varied to produce each syllable in either a high, low, or neutral pitch environment. In a high-pitch environment, F0 following voiceless obstruents is significantly increased relative to the baseline /m/, but following voiced obstruents it closely traces the baseline. In a low-pitch environment, F0 is very slightly increased following all obstruents, voiced and unvoiced. It is suggested that for certain pitch environments a conflict can occur between gestures corresponding to the segmental feature [stiff vocal folds] and intonational elements. The results are different acoustic manifestations of [stiff] in different pitch environments. The spreading of the vocal folds that occurs during unvoiced stops in certain contexts in English is an enhancing gesture, which aids the resolution of the gestural conflict by allowing the defining segmental gesture to be weakened without losing perceptual salience.

Finding speech formants and modulations via energy separation: with application to a vocoder

An experimental system that uses an energy-tracking operator and a related energy separation algorithm to find speech formants and amplitude/frequency modulations automatically in voiced speech segments is presented. Initial estimates of formant center frequencies are provided by either LPC (linear predictive coding) or morphological spectral peak picking. These estimates are improved by a combination of bandpass filtering and iterative application of energy separation. The system is shown to be effective. Its application to an AM-FM vocoder is also discussed.<<ETX>>

Individual variations in glottal characteristics of female speakers

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.

Development of rules for controlling the HLsyn speech synthesizer

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.

Vowel amplitude variation during sentence production

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.

Modeling stop‐consonant releases for synthesis

Poster presented at the Spring 2000 Meeting of the Acoustical Society of America held in Atlanta, GA.

New parameters and mapping relations for the HLsyn speech synthesizer

HLsyn is a quasiarticulatory speech synthesizer in which a small set of parameters control a Klatt synthesizer [Stevens and Bickley, J. Phon. 19 (1991)]. Originally, ten parameters were used. In this paper three new physiologically based parameters, together with some additional modifications, are described. The first is a time‐varying subglottal pressure parameter, which provides the user with additional control of the voice‐source amplitude. It can also be used to turn on voicing, and it has an influence on fundamental frequency. The second parameter is a time‐varying percentage change in the compliances of the vocal‐tract walls and vocal folds. This parameter can, for example, be employed when synthesizing voiced obstruents: increasing it results in facilitation of glottal vibration and lowering of the fundamental frequency. The third parameter is the time‐varying cross‐sectional area of a posterior glottal chink. Because it is independent of the area at the membranous folds, significant noise‐source a...