Quantitative assessment of second language learners' fluency by means of automatic speech recognition technology.

To determine whether expert fluency ratings of read speech can be predicted on the basis of automatically calculated temporal measures of speech quality, an experiment was conducted with read speech of 20 native and 60 non-native speakers of Dutch. The speech material was scored for fluency by nine experts and was then analyzed by means of an automatic speech recognizer in terms of quantitative measures such as speech rate, articulation rate, number and length of pauses, number of dysfluencies, mean length of runs, and phonation/time ratio. The results show that expert ratings of fluency in read speech are reliable (Cronbach's alpha varies between 0.90 and 0.96) and that these ratings can be predicted on the basis of quantitative measures: for six automatic measures the magnitude of the correlations with the fluency scores varies between 0.81 and 0.93. Rate of speech appears to be the best predictor: correlations vary between 0.90 and 0.93. Two other important determinants of reading fluency are the rate at which speakers articulate the sounds and the number of pauses they make. Apparently, rate of speech is such a good predictor of perceived fluency because it incorporates these two aspects.

Stuttering and communicative suitability of speech.

The purpose of the present study was to develop and evaluate an instrument for assessing the communicative suitability of speech (i.e., the speaking situation-dependent adequacy of speech as judged by listeners). Listeners judged the suitability of speech of people who stutter (N = 10) at three stages of treatment (before, immediately after, and 6 months after) and that of people who do not stutter (N = 10, the latter serving as a reference). The listeners rated the suitability of the speech, using a 10-point scale, for 10 speaking situations that supposedly make different demands, with listeners consisting of three groups: unsophisticated listeners (N = 17), clinicians specializing in the treatment of stuttering (N = 17), and stuttering listeners (N = 17). Results indicate that the rating instrument can be scored reliably. Analysis of variance for the ratings of the reference speakers showed that the factor "situation" had a significant effect on the suitability ratings, with more demanding situations receiving lower suitability scores than the less demanding ones. Also, the speech of the people who stutter was judged significantly less suitable than the speech of the reference speakers. Furthermore, unsophisticated listeners were considerably less tolerant in their judgments than clinicians and stuttering listeners. Findings suggest that communicative suitability is a promising criterion to further investigate, especially as it may apply to the objective evaluation of treatment outcome for stuttering.

Perceptual rating instrument for speech evaluation of stuttering treatment.

A rating instrument is described that can be used to assess the results of stuttering treatments. The instrument is designed for use with naive listeners. It yields a comprehensive and detailed description of the speech quality in terms of articulation, phonation, pitch, and loudness; in addition, it includes a naturalness scale. Analysis of ratings obtained with the instrument show that naturalness is a multidimensional characteristic. Moreover, the speech characteristics that determine the naturalness ratings appear to be different pretreatment, posttreatment, and at follow-up treatment. The psychometric characteristics of the instrument are analyzed in detail. It is concluded that mixing of samples of stutterers and nonstutterers in one rating experiment may artificially inflate the reliability of the ratings. Also, ratings on equal-appearing interval scales cannot be interpreted in an absolute sense. Solutions for this methodological problem are suggested.

Coordination of aerodynamic and phonatory processes in fluent speech utterances of stutterers.

It has often been suggested that there is a close relation between problems in the coordination of respiratory, phonatory, and articulatory processes and dysfluencies in speech production. However, empirical support for this hypothesis is scarce, because most studies of speech behavior have been restricted to a single motor process. The present investigation examines the interactions of respiration (specifically the build up of subglottal pressure), phonation, and articulation. Pressure build-up patterns preceding the onset of phonation were studied in 573 fluent utterances of 10 stutterers and in 552 utterances of 7 control subjects. Stutterers evidenced deviant patterns of subglottal pressure build-up much more often than did control speakers. Electroglottographic records of voice onset were classified as either abrupt or gentle and with respect to the presence or absence of gross irregularities in amplitude (shimmer) and period duration (jitter). Stutterers evidenced abrupt voice onsets significantly more often than did controls. The occurrence of jitter and shimmer, however, did not differ significantly across the groups. Acoustic measures of abruptness of voice onset, first syllable duration, and average syllable duration were also obtained, but they failed to differ significantly between the two groups. This study corroborates previous findings that perceptually fluent utterances of stutterers may differ, on a physiological level, from the speech of nonstutterers.

On the measurement of glottal flow.

For developing a comprehensive description of voiced speech sounds in terms of a phonation and an articulation component, it is necessary to know to what extent the volume flow modulations at the entrance of the vocal tract are due to vocal fold motions and to what extent they are due to variations in the transglottal pressure. In order to be able to study this problem, it is important that the flow at the glottis can be measured during normal speech production in a reliable fashion. In this article, a flow measurement technique is described that differs from the more usual inverse filtering approach to the extent that the flow is not measured at the mouth, but much closer to the glottis. The technique is based on the measurement of pressure gradient. It is shown that the proposed method also leads to an inverse filtering problem, but that, since this problem is much simpler, the gradient method yields more reliable estimates of the shape of the glottal flow waveform, though without the zero flow level (dc component) and without a magnitude scale. By means of theoretical considerations about velocity profiles in pulsatile flow in cylindrical tubes, it is shown that the method for measuring flow during phonation proposed in this article may be expected to yield reasonable flow waveform estimates in a frequency region from any normal fundamental frequency to an upper frequency determined by the transducer sensitivity and separation and vocal tract geometry. In this case, the frequency limitation was estimated to be 1000 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

On subglottal formant analysis.

When subglottal pressure signals which are recorded during normal speech production are spectrally analyzed, the frequency of the first spectral maximum appears to deviate appreciably from the first resonance frequency which has been reported in the literature and which stems from measurements of the acoustic impedance of the subglottal system. It is postulated that this is caused by the spectrum of the excitation function. This hypothesis is corroborated by a modeling study. Using an extended version of the well-known two-mass model of the vocal folds that can account for a glottal leak, it is shown that under realistic physiological assumptions glottal flow waveforms are generated whose spectral properties cause a downward shift of the location of the first spectral maximum in the subglottal pressure signals. The order of magnitude of this effect is investigated for different glottal settings and with a subglottal system that is modeled according to the impedance measurements reported in the literature. The outcomes of this modeling study show that the location of the first spectral maximum of the subglottal pressure may deviate appreciably from the natural frequency of the subglottal system. As a consequence, however, the comfortable assumption that in normal speech the glottal excitation function is constant and zero during the "closed glottis interval" has to be called into question.

Perceptual judgment of abruptness of voice onset in vowels as a function of the amplitude envelope.

Four experienced speakers were trained to produce isolated vowels with different degrees of abruptness of voice onset while keeping the maximum sound level and the duration of the sounds constant. A total of 420 vowel tokens were rated for abruptness of voice onset by 11 trained speech scientists in order to study the reliability of the ratings, which was found to be moderately high (r1,1 = .74 with an extremely large range of the stimuli). Next a number of simple descriptions of the rising slope of the amplitude envelope are developed. It appears that the logarithm of the time needed for the amplitude envelope to rise from 10% to 90% of its eventual maximum level is the best predictor of perceived abruptness of voice onset of the measures examined in this study. Based on this result, an inexpensive instrument is described that can help the speech-language pathologist in assessing abruptness of voice onset in clinical practice.

The effects of low-pass filtering and random splicing on the perception of speech.

In this paper the results are presented of an auditory description of 32 nonmanipulated, low-pass-filtered, and random-spliced speech samples. The description consisted of the ratings by three raters on 24 speech scales. The aim of this study was to establish the effects of the manipulations on the perception of speech. Insight into this question was gained by examining the reliability of, and the correlations between, the ratings in the three conditions, and by considering the outcomes of a number of t tests. It appeared that, after filtering, in addition to prosodic features, a number of voice quality characteristics remain present in the signal; articulatory information is eliminated. After splicing, not only voice quality features but also some articulatory and prosodic information remain present. Moreover, the study revealed that both content-masking techniques bring about systematic biases in the perception. These findings are relevant to emotion and personality research in which low-pass filtering and random splicing are used as masking techniques.

Pressure measurements during speech production using semiconductor miniature pressure transducers: impact on models for speech production.

It appears that temperature instabilities are a major obstacle hindering the use of semiconductor strain gauge pressure transducers in speech research, especially when absolute pressure data are mandatory. In this paper a simple and reliable method for an in vivo calibration of this kind of transducer is described. The most important error source, the drift of the zero pressure level due to temperature changes, is discussed, and an estimation of the measurement accuracy which can be obtained is given. Moreover, some registrations of subglottal, supraglottal, and transglottal pressure are presented. It is shown that the pressure recordings allow us to obtain estimates of the volume flow in the trachea and pharynx. Analysis of those waveforms appears to lead to new insights into the physical processes underlying voice production. Specifically, an independent glottal contribution to the skewing of the glottal flow pulses is identified.