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Previous studies of the effect of vowel context on fricatives showseeming contradictions in the case of /s/: acoustic analysis shows the greatest context effect, while aerodynamic analysis shows relatively little effect, for the same subject. In this study, aerodynamic, acoustic, and articulatory data for the same subject producing /s, z/ in a variety of contexts were compared systematically. The strong acoustic effect of the /u - u/ context exists with /z/ as well as /s/, and appears to arise from a whistle-like source mechanism caused by lip rounding; the main tongue constriction does appear to be immune to vowel context. Our interpretation of aerodynamic data as constrictions in series can be generalized to include the influence of lip rounding, thus: for this speaker and for these speech-like sequences, the area of the vocal tract constriction for /s/ is independent of the vowel context but the overall aerodynamic effect does vary with lip rounding. Our aerodynamic and acoustic data seem to be consistent; both support the view that some rounding extends into the /s/ fricative.

Articulatory paths have been analysed for the frictive [s] produced by a woman speaker of General American English in connected speech and also in phonotically controlled speech-like sequencues at a shower speech rate. Aerodynamically derived traces indicating the acoustically relevant parameter of cross-section area of the constricted region of the vocal tract suggested that, contrary to related data for the movements of the solid structures, some portions of the traces for this vocal tract indicator had the same path shape across some different vowel contexts and across different speech styles. In the connected speech, the whole cross-section area path seemed to be invariant across different stressed vowel contexts. The acoustic pattern features associated with the invariant portions of vocal tract articulation, in combination with appropriate respiratory and laryngeal articulations, are discussed.

The importance of overlapping coordinated gestures in achieving the auditory goals of speech is considered. Articulatory synthesis can help our understanding of the coordination problems and the variety of solutions found by real speakers. The time required to perform specific essential gestures, such as abduction-adduction of the vocal folds for fricatives, imposes strong timing constraints. In different speech sequences different articulators act as the duration-determining factor (DDF). Timing variability needs to be modelled also. Further experimentation is needed to determine whether increased speaking rate more nearly retains constant phase or constant absolute durational separation of articulatory events and whether or not some gestures can disappear under the relaxed auditory criteria of a casual style of speech. Two examples are presented, from the Leeds articulatory modelling, of the ways in which the phonological system of the language interacts with the processes and constraints of the speech production system to yield context-dependent variation for individual phonemes.

Covarying acoustic pattern features located near the boundary region between a frication noise segment and the adjacent vocoid (vocalic) segments seem likely to be important for the intelligibility of fricative consonants. Attempts to capture some of these naturally occurring effects through simulation with a computer-implemented composite model of speech production are described. The aim is to gain greater understanding of the production of fricatives, by trying to match quantitatively the detailed patterning for each of two speakers. An analysis-by-synthesis approach is adopted: parameters in the model are first given estimated values based on the analysis of some phonetically controlled [vowel-fricative-vowel] sequences produced by the speaker; in subsequent runs of the model the match can be improved. First results for one speaker's production of [asa] are described.

Simple articulatory contrasts for a phonological opposition generate a multiplicity of acoustic cues. Knowledge of the covariations of acoustic pattern features within and across speakers is needed for automatic speech recognition. A model of speech production processes was used to generate stimuli along an articulatory continuum, the degree of abduction of the vocal folds for the fricatives in English words “hiss” and “his”. Transition times imposed strong constraints on the articulatory plans devised as inputs to the model. Acoustic segment durations output from the model covaried in the same way as those produced by 5 real speakers; there was good quantitative agreement in most cases. Listeners' responses suggest that the articulatory dimension synthesised is a suitable one for natural speech. Future directions for the modelling of multiple articulatory dimensions and for mapping from speaker-specific patterns of articulation and their perturbations onto the stability of particular acoustic cues are discussed.

A composite model of speech production has been used to try to match the articulatory, aerodynamic and acoustic patterns for some real speakers of British English. The aim is to characterize particular speakers or speaker types acoustically through a match to their individual articulatory actions. In the model, the larynx contributes two independent articulatory actions; in addition it generates the acoustic source for voicing. The problems of direct matching of acoustic patterns are very great. The particular advantage of the analysis-by-synthesis methods described here is that the aerodynamic stage, which links actions to sounds, is included. As a result, the articulatory match can be made with some confidence before acoustic source and filter properties are varied; acoustic sources and acoustic pattern features of the synthetic speech co-vary in ways similar to those observed in natural speech. The model has been used to simulate disordered as well as normal larynx behaviour.

Links are needed to bridge the gap between the analysis of speech as a set of discrete, ordered but durationless linguistic unit and analyses of the continuously changing acoustic signals, defined along a time axis. Current recognition and synthesis devices do not make good use of the structure imposed by speech production processes on the mapping between an allophone sequence and the many possible associated speech signals. A quantitative, flexible articulatory time framework has been developed as a contribution to the new kinds of phonetic descriptions needed. Units of articulation for allophones of the phonemes of British English and methods for linking adjacent allophones are proposed. Tentative specifications for a sub-set are offered, based on a review of published findings for natural speech. Articulatory schemes are taken to be organised with reference to particular events E . Pairs of events need to be appropriately coordinated in time. The two events may relate to inter-articulator coordination between two different quasi-independent articulators or to the durational extent of a statically maintained state for a single articulator. The coordination between the two events is expressed through the duration D of the time interval between them. Six examples are given of the construction of a complete articulatory time plan for an English sequence. This forms the first stage for a computer-implemented model of the articulatory, aerodynamic and acoustic processes of speech production. The synthetic speech output from the model is given acoustic variations intended to mimic those arising in natural speech due to a speaker's choice of options, including a change in rate of speech. This is achieved in the modelling by altering one or more D values in the articulatory time plan and by dispensing with some optional actions. The variability of multiple repetitions by a real speaker can be introduced into the synthetic speech by perturbing the D values. The model needs to be matched to specific real speakers in order to assess the extent to which it is realistic in its simulation of the variation and variability of acoustic pattern features for natural speech and the extent to which covariations can be predicted with it.

In his book An Introduction to the Pronunciation of English A. C. Gimson (1970) describes the articulation of the English plosives in different phonetic contexts. He demonstrates here (146–54 and 156–8) and elsewhere (Gimson, 1960) the articulatory instability of, in particular, the alveolar plosives /t/ and /d/ in English. As W. S. Allen (1960) points out, the predominance of instability associated with the alveolar plosives, rather than with the bilabials /p/ and /b/ or velars /k/ and /g/ may correlate with the more common occurrence of the alveolars rather than with articulatory or other kinds of constraints specific to consonantal clusters containing /t/ and /d/.

An experiment in which oral pressure and volume flow of air through the mouth were measured simultaneously for one speaker of English has shown that: (1) the timing of the tongue movements for /s/ and /z/ is the same when similar phonetic contexts are compared; (2) air flow and pressure are both significantly greater for /s/ than for /z/, in agreement with previous work; but (3) aerodynamic measures indicating the degree of tongue occlusion show no significant difference between /s/ and /z/. The feature tense-lax operates in the expected way at the acoustic stage for /s/ and /z/, but applies, at the articulatory stage, either not at all, or else in the opposite direction to that expected. Experiments with the same speaker, including oesophageal pressure measurements to indicate tracheal pressure, support the view that the only significant difference in the articulation of these /s/ and /z/ segments lies in the glottal adjustment and not in muscular effort defined in any other way, nor in breath force. The observed acoustic effects follow automatically from the different oral pressures and air flows, which are the direct result of the different glottal articulations.