Effect of speaking rate on vowel formant movements

The purpose of this experiment was to study the effects of changes in speaking rate on both the attainment of acoustic vowel targets and the relative time and speed of movements toward these presumed targets. Four speakers produced a number of different CVC and CVCVC utterances at slow and fast speaking rates. Spectrographic measurements showed that the midpoint format frequencies of the different vowels did not vary as a function of rate. However, for fast speech the onset frequencies of second formant transitions were closer to their target frequencies while CV transition rates remained essentially unchanged, indicating that movement toward the vowel simply began earlier for fast speech. Changes in both speaking rate and lexical stress had different effects. For stressed vowels, an increase in speaking rate was accompanied primarily by a decrease in duration. However, destressed vowels, even if they were of the same duration as quickly produced stressed vowels, were reduced in overall amplitude, fundamental frequency, and to some extent, vowel color. These results suggest that speaking rate and lexical stress are controlled by two different mechanisms.     

Effect of speaking rate and contrastive stress on formant dynamics and vowel perception

Vowel formants play an important role in speech theories and applications; however, the same formant values measured for the steady-state part of a vowel can correspond to different vowel categories. Experimental evidence indicates that dynamic information can also contribute to vowel characterization. Hence, dynamically modeling formant transitions may lead to quantitatively testable predictions in vowel categorization. Because the articulatory strategy used to manage different speaking rates and contrastive stress may depend on speaker and situation, the parameter values of a dynamic formant model may vary with speaking rate and stress. In most experiments speaking rate is rarely controlled, only two or three rates are tested, and most corpora contain just a few repetitions of each item. As a consequence, the dependence of dynamic models on those factors is difficult to gauge. This article presents a study of 2300 [iai] or [i epsilon i] stimuli produced by two speakers at nine or ten speaking rates in a carrier sentence for two contrastive stress patterns. The corpus was perceptually evaluated by naive listeners. Formant frequencies were measured during the steady-state parts of the stimuli, and the formant transitions were dynamically and kinematically modeled. The results indicate that (1) the corpus was characterized by a contextual assimilation instead of a centralization effect; (2) dynamic or kinematic modeling was equivalent as far as the analysis of the model parameters was concerned; (3) the dependence of the model parameter estimates on speaking rate and stress suggests that the formant transitions were sharper for high speaking rate, but no consistent trend was found for contrastive stress; (4) the formant frequencies measured in the steady-state parts of the vowels were sufficient to explain the perceptual results while the dynamic parameters of the models were not.     

Effects of speaking rate on second formant trajectories of selected vocalic nuclei

The effect of speaking rate variations on second formant (F2) trajectories was investigated for a continuum of rates. F2 trajectories for the schwa preceding a voiced bilabial stop, and one of three target vocalic nuclei following the stop, were generated for utterances of the form "Put a bV here, where V was /i/,/ae/ or /oI/. Discrete spectral measures at the vowel-consonant and consonant-vowel interfaces, as well as vowel target values, were examined as potential parameters of rate variation; several different whole-trajectory analyses were also explored. Results suggested that a discrete measure at the vowel consonant (schwa-consonant) interface, the F2off value, was in many cases a good index of rate variation, provided the rates were not unusually slow (vowel durations less than 200 ms). The relationship of the spectral measure at the consonant-vowel interface, F2 onset, as well as that of the "target" for this vowel, was less clearly related to rate variation. Whole-trajectory analyses indicated that the rate effect cannot be captured by linear compressions and expansions of some prototype trajectory. Moreover, the effect of rate manipulation on formant trajectories interacts with speaker and vocalic nucleus type, making it difficult to specify general rules for these effects. However, there is evidence that a small number of speaker strategies may emerge from a careful qualitative and quantitative analysis of whole formant trajectories. Results are discussed in terms of models of speech production and a group of speech disorders that is usually associated with anomalies of speaking rate, and hence of formant frequency trajectories.     

Effect of cognitive load on articulation rate and formant frequencies during simulator flights

It was explored how three types of intensive cognitive load typical of military aviation (load on situation awareness, information processing, or decision-making) affect speech. The utterances of 13 male military pilots were recorded during simulated combat flights. Articulation rate was calculated from the speech samples, and the first formant (F1) and second formant (F2) were tracked from first-syllable short vowels in pre-defined phoneme environments. Articulation rate was found to correlate negatively (albeit with low coefficients) with loads on situation awareness and decision-making but not with changes in F1 or F2. Changes were seen in the spectrum of the vowels: mean F1 of front vowels usually increased and their mean F2 decreased as a function of cognitive load, and both F1 and F2 of back vowels increased. The strongest associations were seen between the three types of cognitive load and F1 and F2 changes in back vowels. Because fluent and clear radio speech communication is vital to safety in aviation and temporal and spectral changes may affect speech intelligibility, careful use of standard aviation phraseology and training in the production of clear speech during a high level of cognitive load are important measures that diminish the probability of possible misunderstandings.     

Influence of speaking rate on the upper lip, lower lip, and jaw peak velocity sequencing during bilabial closing movements

Upper lip, lower lip, and jaw movements were recorded in five adult speakers for repeated sequences of the utterance [bae] at different speech rates. The results failed to confirm several earlier reports of an invariant upper lip, lower lip, jaw peak velocity sequencing pattern for bilabial closures. While the earlier reported sequence was the most frequent, a wide variety of different sequences was also commonly observed. In addition, significant intersubject differences in sequencing were found. The present results thus do not support the earlier hypothesis that oral closure gestures reflect aspects of a centrally generated pattern of motor output during speech.     

Perceptual invariance of coarticulated vowels over variations in speaking rate

This study examined the perception and acoustics of a large corpus of vowels spoken in consonant-vowel-consonant syllables produced in citation-form (lists) and spoken in sentences at normal and rapid rates by a female adult. Listeners correctly categorized the speaking rate of sentence materials as normal or rapid (2% errors) but did not accurately classify the speaking rate of the syllables when they were excised from the sentences (25% errors). In contrast, listeners accurately identified the vowels produced in sentences spoken at both rates when presented the sentences and when presented the excised syllables blocked by speaking rate or randomized. Acoustical analysis showed that formant frequencies at syllable midpoint for vowels in sentence materials showed "target undershoot" relative to citation-form values, but little change over speech rate. Syllable durations varied systematically with vowel identity, speaking rate, and voicing of final consonant. Vowel-inherent-spectral-change was invariant in direction of change over rate and context for most vowels. The temporal location of maximum F1 frequency further differentiated spectrally adjacent lax and tense vowels. It was concluded that listeners were able to utilize these rate- and context-independent dynamic spectrotemporal parameters to identify coarticulated vowels, even when sentential information about speaking rate was not available.     

Perceived speech rate: the effects of articulation rate and speaking style in spontaneous speech

In this study, the effect of articulation rate and speaking style on the perceived speech rate is investigated. The articulation rate is measured both in terms of the intended phones, i.e., phones present in the assumed canonical form, and as the number of actual, realized phones per second. The combination of these measures reflects the deletion of phones, which is related to speaking style. The effect of the two rate measures on the perceived speech rate is compared in two listening experiments on the basis of a set of intonation phrases with carefully balanced intended and realized phone rates, selected from a German database of spontaneous speech. Because the balance between input-oriented (effort) and output-oriented (communicative) constraints may be different at fast versus slow speech rates, the effect of articulation rate is compared both for fast and for slow phrases from the database. The effect of the listeners' own speaking habits is also investigated to evaluate if listeners' perception is based on a projection of their own behavior as a speaker. It is shown that listener judgments reflect both the intended and realized phone rates, and that their judgments are independent of the constraint balance and their own speaking habits.     

汉语连续语音识别的语速自适应算法

在连续语音中,不同的说话者在不同语境下说话的速度差异是很大的。偏离正常语速往往会造成识别错误,使识别性能下降。考虑到语速对于语音单元段长的影响是同步增长或同步下降的,相邻语音单元的段长之间存在很强的相关性,本文从利用段长的相关信息出发,在基于段长分布的隐含马尔可夫模型(DDBHMM:Duration Distribution Based HMM)的框架上,提出了一种语速自适应算法。对数字串和大词汇量连续语音识别的试验表明这个算法是有效的。     

Articulatory correlates of stress and speaking rate in Swedish VCV utterances

Articulatory activity underlying changes in stress and speaking rate was studied by means of x-ray cinefilm and acoustic speech records. Two Swedish subjects produced vowel-consonant-vowel (VCV) utterances under controlled rate-stress conditions. The vowels were tense (i a u), and the consonants were the voiceless stops, notably (p). The spectral characteristics of the vowels were not significantly influenced by changes in the speaking rate. They were, however, significantly emphasized under stress. At the articulatory level, stressed vowels displayed narrower oral tract constrictions than unstressed vowels at the two speaking rates studied. At the faster speaking rate, vowel- and consonant-related gestures were coproduced to a greater extent than at the slower rate. The data, failing to produce evidence for an "undershoot" mechanism, support the view that dialect-specific correlates of stress are actively safeguarded by means of articulatory reorganization.     

Effects of speaking rate on tongue position and velocity of movement in vowel production

This study used glossometry to examine the position of the tongue and the velocity of its movements in vowels spoken normally and at a self-selected fast rate. The subject in experiment 1 showed lingual undershoot for stressed vowels in "a big again" and "a bob again." The tongue was lower for /I/ and higher for /a/ at the fast rate than at the normal rate. The stressed vowels exerted an affect on unstressed vowels: The tongue was lower in the schwas that preceded and followed /a/ than /I/. Only one of the three subjects in experiment 2 showed no lingual undershoot for fast-rate /I/. The tongue was higher at the fast rate than at the normal rate in the schwas flanking /I/ so that the displacement was less at the fast rate than at the normal rate. Another talker increased the peak velocity of tongue movements at the fast rate and showed no undershoot for /a/. Multiple regression analyses showed that the timing of movements for successive phonetic segments accounted well for undershoot in only one of the three subjects. The results suggest that in order to model the effects of speaking rate on the tongue movements used in forming stressed vowels, it will be necessary to take into account: (1) how much vowels are shortened at a fast rate: (2) how much the peak velocity of tongue movements is increased, if at all; and (3) the position of the tongue before and after the stressed vowels. All three factors are likely to be influenced by how clearly the talker wishes to speak.     

Adaptive control of vowel formant frequency: evidence from real-time formant manipulation

Auditory feedback during speech production is known to play a role in speech sound acquisition and is also important for the maintenance of accurate articulation. In two studies the first formant (F1) of monosyllabic consonant-vowel-consonant words (CVCs) was shifted electronically and fed back to the participant very quickly so that participants perceived the modified speech as their own productions. When feedback was shifted up (experiment 1 and 2) or down (experiment 1) participants compensated by producing F1 in the opposite frequency direction from baseline. The threshold size of manipulation that initiated a compensation in F1 was usually greater than 60 Hz. When normal feedback was returned, F1 did not return immediately to baseline but showed an exponential deadaptation pattern. Experiment 1 showed that this effect was not influenced by the direction of the F1 shift, with both raising and lowering of F1 exhibiting the same effects. Experiment 2 showed that manipulating the number of trials that F1 was held at the maximum shift in frequency (0, 15, 45 trials) did not influence the recovery from adaptation. There was a correlation between the lag-one autocorrelation of trial-to-trial changes in F1 in the baseline recordings and the magnitude of compensation. Some participants therefore appeared to more actively stabilize their productions from trial-to-trial. The results provide insight into the perceptual control of speech and the representations that govern sensorimotor coordination.     

Control of rate and duration of speech movements

A computerized pulsed-ultrasound system was used to monitor tongue dorsum movements during the production of consonant-vowel sequences in which speech rate, vowel, and consonant were varied. The kinematics of tongue movement were analyzed by measuring the lowering gesture of the tongue to give estimates of movement amplitude, duration, and maximum velocity. All three subjects in the study showed reliable correlations between the amplitude of the tongue dorsum movement and its maximum velocity. Further, the ratio of the maximum velocity to the extent of the gesture, a kinematic indicator of articulator stiffness, was found to vary inversely with the duration of the movement. This relationship held both within individual conditions and across all conditions in the study such that a single function was able to accommodate a large proportion of the variance due to changes in movement duration. As similar findings have been obtained both for abduction and adduction gestures of the vocal folds and for rapid voluntary limb movements, the data suggest that a wide range of changes in the duration of individual movements might all have a similar origin. The control of movement rate and duration through the specification of biomechanical characteristics of speech articulators is discussed.     

Experimental manipulation of speaking rate for studying temporal variability in children's speech

Children's speech timing is often more variable than adults'. In the present study, two hypotheses that have been proposed to account for this observation are considered. One claims that children do not have neuromotor control capabilities comparable to adults. The other suggests that the greater variability is a statistical consequence of children's longer segment durations. These two hypotheses were examined by having children and adults speak at both faster and slower rates than normal. Within-group comparisons across different rates and between-group comparisons for similar durational values were made from spectrographic measurements. Results indicate that both statistical and neuromotor factors seem to contribute to the greater variability commonly observed in children's speech.     

Effects of consonant environment on vowel formant patterns

A significant body of evidence has accumulated indicating that vowel identification is influenced by spectral change patterns. For example, a large-scale study of vowel formant patterns showed substantial improvements in category separability when a pattern classifier was trained on multiple samples of the formant pattern rather than a single sample at steady state [J. Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099-3111 (1995)]. However, in the earlier study all utterances were recorded in a constant /hVd/ environment. The main purpose of the present study was to determine whether a close relationship between vowel identity and spectral change patterns is maintained when the consonant environment is allowed to vary. Recordings were made of six men and six women producing eight vowels (see text) in isolation and in CVC syllables. The CVC utterances consisted of all combinations of seven initial consonants (/h,b,d,g,p,t,k/) and six final consonants (/b,d,g,p,t,k/). Formant frequencies for F1-F3 were measured every 5 ms during the vowel using an interactive editing tool. Results showed highly significant effects of phonetic environment. As with an earlier study of this type, particularly large shifts in formant patterns were seen for rounded vowels in alveolar environments [K. Stevens and A. House, J. Speech Hear. Res. 6, 111-128 (1963)]. Despite these context effects, substantial improvements in category separability were observed when a pattern classifier incorporated spectral change information. Modeling work showed that many aspects of listener behavior could be accounted for by a fairly simple pattern classifier incorporating F0, duration, and two discrete samples of the formant pattern.     

Effect of different types of auditory stimulation on vowel formant frequencies in multichannel cochlear implant users

Two experiments investigating the effects of auditory stimulation delivered via a Nucleus multichannel cochlear implant upon vowel production in adventitiously deafened adult speakers are reported. The first experiment contrasts vowel formant frequencies produced without auditory stimulation (implant processor OFF) to those produced with auditory stimulation (processor ON). Significant shifts in second formant frequencies were observed for intermediate vowels produced without auditory stimulation; however, no significant shifts were observed for the point vowels. Higher first formant frequencies occurred in five of eight vowels when the processor was turned ON versus OFF. A second experiment contrasted productions of the word "head" produced with a FULL map, OFF condition, and a SINGLE channel condition that restricted the amount of auditory information received by the subjects. This experiment revealed significant shifts in second formant frequencies between FULL map utterances and the other conditions. No significant differences in second formant frequencies were observed between SINGLE channel and OFF conditions. These data suggest auditory feedback information may be used to adjust the articulation of some speech sounds.     

Stimulus variability and the phonetic relevance hypothesis: effects of variability in speaking style, fundamental frequency, and speaking rate on spoken word identification

Three experiments were conducted to examine the effects of trial-to-trial variations in speaking style, fundamental frequency, and speaking rate on identification of spoken words. In addition, the experiments investigated whether any effects of stimulus variability would be modulated by phonetic confusability (i.e., lexical difficulty). In Experiment 1, trial-to-trial variations in speaking style reduced the overall identification performance compared with conditions containing no speaking-style variability. In addition, the effects of variability were greater for phonetically confusable words than for phonetically distinct words. In Experiment 2, variations in fundamental frequency were found to have no significant effects on spoken word identification and did not interact with lexical difficulty. In Experiment 3, two different methods for varying speaking rate were found to have equivalent negative effects on spoken word recognition and similar interactions with lexical difficulty. Overall, the findings are consistent with a phonetic-relevance hypothesis, in which accommodating sources of acoustic-phonetic variability that affect phonetically relevant properties of speech signals can impair spoken word identification. In contrast, variability in parameters of the speech signal that do not affect phonetically relevant properties are not expected to affect overall identification performance. Implications of these findings for the nature and development of lexical representations are discussed.     

语谱图共振峰的自动跟踪算法

本文介绍一个共振峰轨迹的自动跟踪算法，其特点是不借助于其它的信息来源，仅仅是基于语谱图信息，来确定语谱图上前四个共振峰频率的位置和它们关于时间轴的轨迹。算法由三个层面构成；第一层面是进行频率分布的分析，以决定一个最佳的共振峰搜索起始位置；第二层面是采用双搜索算法，来跟踪随时间变化的共振峰轨迹；第三层面是解决某些冲突现象，在共振峰跟踪问题上的难点之一是处理多个共振峰的合并现象和冗余峰值现象。     

一种新的基于倒谱的共振峰频率检测算法

共振峰频率是语音信号的一个重要参数。传统的基于线性预测的共振峰检测算法由于受到计算量的限制,很难实现实时处理。本文提出一种基于倒谱变换的共振峰频率检测算法,采用后置处理,比较声道冲击响应对数幅频特性的二次导数和相频特性一次导数检测出的结果,删除伪峰数值和甄别合并共振峰,提高检测精度。仿真结果证明,该算法计算效率高,低信噪比下仍能保持较好的检测性能。