Michael J. Clark

Acoustic characteristics of American English vowels

The purpose of this study was to replicate and extend the classic study of vowel acoustics by Peterson and Barney (PB) [J. Acoust. Soc. Am. 24, 175-184 (1952)]. Recordings were made of 45 men, 48 women, and 46 children producing the vowels /i,I,e, epsilon,ae,a, [symbol: see text],O,U,u, lambda,3 iota/ in h-V-d syllables. Formant contours for F1-F4 were measured from LPC spectra using a custom interactive editing tool. For comparison with the PB data, formant patterns were sampled at a time that was judged by visual inspection to be maximally steady. Analysis of the formant data shows numerous differences between the present data and those of PB, both in terms of average frequencies of F1 and F2, and the degree of overlap among adjacent vowels. As with the original study, listening tests showed that the signals were nearly always identified as the vowel intended by the talker. Discriminant analysis showed that the vowels were more poorly separated than the PB data based on a static sample of the formant pattern. However, the vowels can be separated with a high degree of accuracy if duration and spectral change information is included.

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.

Some effects of duration on vowel recognition

This study was designed to examine the role of duration in vowel perception by testing listeners on the identification of CVC syllables generated at different durations. Test signals consisted of synthesized versions of 300 utterances selected from a large, multitalker database of /hVd/ syllables [Hillenbrand et al., J. Acoust. Soc. Am. 97, 3099-3111 (1995)]. Four versions of each utterance were synthesized: (1) an original duration set (vowel duration matched to the original utterance), (2) a neutral duration set (duration fixed at 272 ms, the grand mean across all vowels), (3) a short duration set (duration fixed at 144 ms, two standard deviations below the mean), and (4) a long duration set (duration fixed at 400 ms, two standard deviations above the mean). Experiment 1 used a formant synthesizer, while a second experiment was an exact replication using a sinusoidal synthesis method that represented the original vowel spectrum more precisely than the formant synthesizer. Findings included (1) duration had a small overall effect on vowel identity since the great majority of signals were identified correctly at their original durations and at all three altered durations; (2) despite the relatively small average effect of duration, some vowels, especially [see text] and [see text], were significantly affected by duration; (3) some vowel contrasts that differ systematically in duration, such as [see text], and [see text], were minimally affected by duration; (4) a simple pattern recognition model appears to be capable of accounting for several features of the listening test results, especially the greater influence of duration on some vowels than others; and (5) because a formant synthesizer does an imperfect job of representing the fine details of the original vowel spectrum, results using the formant-synthesized signals led to a slight overestimate of the role of duration in vowel recognition, especially for the shortened vowels.

The role of f (0) and formant frequencies in distinguishing the voices of men and women.

The purpose of the present study was to determine the contributions of fundamental frequency (f0) and formants in cuing the distinction between men’s and women’s voices. A source-filter synthesizer was used to create four versions of 25 sentences spoken by men: (1) unmodified synthesis, (2) f0 only shifted up toward values typical of women, (3) formants only shifted up toward values typical of women, and (4) both f0 and formants shifted up. Identical methods were used to generate four corresponding versions of 25 sentences spoken by women, but with downward shifts. Listening tests showed that (1) shifting both f0 and formants was usually effective (∼82%) in changing the perceived sex of the utterance, and (2) shifting either f0 or formants alone was usually ineffective in changing the perceived sex. Both f0 and formants are apparently needed to specify speaker sex, though even together these cues are not entirely effective. Results also suggested that f0 is somewhat more important than formants. A second experiment used the same methods, but isolated /hVd/ syllables were used as test signals. Results were broadly similar, with the important exception that, on average, the syllables were more likely to shift perceived talker sex with shifts in f0 and/or formants.

Quality of American English front vowels before /r/

The vowels /i/ and / I / are not contrastive before /r/ in American English, and the phonetics literature is equivocal about which symbol to use for the nucleus in words such as beer . Similarly /e/ and /e/ are not contrastive before /r/, and the literature contains varied references to one or the other in words such as bear . The purpose of this study was to investigate these vowels by acoustic measurements, discriminant analyses, and listening tests. Eleven men and ten women residing in southern Michigan recorded /r/-final monosyllables ( beer , bear , hear , hair ), as well as words containing /i, I e, e with other finals, such as beet , bit , bait , bet . Acoustic measurements included the first three formants at steady state. The high front vowel in /r/-final syllables ( beer , hear ) showed formant values intermediate between /i/ and / I /, but closer to /i/, and the mid front vowel (in bear and hair ) was intermediate between /e/ and /e/, but closer to /e/. Discriminant analysis using the first three formants and listening tests using 60 ms vowel excerpts yielded results consistent with the idea that the pre-/r/ vowels are acoustically intermediate between their tense and lax neighbors but resemble /i/ and /e/ more closely than / I / and /e/.

Perceptual accommodation to sinewave speech.

Many studies have reported good intelligibility for sine wave replicas of sentences (e.g., R. Remez et al., Science 212, 947–950 (1981)]. Recent work, however, has shown poor intelligibility (∼55%) for vowels in isolated syllables [J. Hillenbrand and M. Clark, J. Acoust. Soc. Am. 123, 3326 (2008)]. While enhanced intelligibility for sentences undoubtedly reveals the importance of top‐down mechanisms, it is also possible that sentence‐length utterances allow listeners to make (as yet unknown) perceptual accommodations to the unfamiliar acoustic properties of sine wave speech (SWS). In this study, the intelligibility of SWS replicas of 16 vowels/diphthongs in isolated syllables (“heed,” “hid,” and “hide”) was compared to that of the same syllables when preceded by a seven‐word SWS carrier phrase (CP) spoken by the same talker. Intelligibility was ∼24 percentage points higher when the SWS syllables were preceded by the SWS CP than when the same utterances were presented in isolation. Furthermore, the effect ...

Quality of front vowels before /r/

The vowels /i/ and /I/ are not contrastive before /r/ in American english, and the phonetics literature is equivocal about which symbol to use for the nucleus in words such as beer. Similarly /e/ and /e/ are not contrastive before /r/, and the literature contains varied references to one or the other in words such as bear. Trained listeners disagree about representing the vowel in /r/‐final words. Ten men and ten women recorded monosyllables containing /i,I,e,e/, with initial /b/ and /h/ and with no final consonant or with final /d/ and /t/. For example, the /b/‐initial high front series was bee, bead, beet, bid, bit. Additionally an /r/‐final set (beer, bear, hear, hair) was recorded. Acoustic measurements included the first two formants. Formants for /i,I,e,e/ in /d/‐final and /t/‐final syllables (and for /i,e/ in open syllables) were typical of those measured in an earlier study of subjects from the same region. The high front vowel in /r/‐final syllables (beer and hear) showed formant values intermedi...

Phonetics Exercises Using the Alvin Experiment-Control Software

PURPOSE Exercises are described that were designed to provide practice in phonetic transcription for students taking an introductory phonetics course. The goal was to allow instructors to offload much of the drill that would otherwise need to be covered in class or handled with paper-and-pencil tasks using text rather than speech as input. METHOD The exercises were developed using Alvin, a general-purpose software package for experiment design and control. The simplest exercises help students learn sound-symbol associations. For example, a vowel-transcription exercise presents listeners with consonant-vowel-consonant syllables on each trial; students are asked to choose among buttons labeled with phonetic symbols for 12 vowels. Several word-transcription exercises are included in which students hear a word and are asked to enter a phonetic transcription. Immediate feedback is provided for all of the exercises. An explanation of the methods that are used to create exercises is provided. RESULTS Although no formal evaluation was conducted, comments on course evaluations suggest that most students found the exercises to be useful. CONCLUSIONS Exercises were developed for use in an introductory phonetics course. The exercises can be used in their current form, they can be modified to suit individual needs, or new exercises can be developed.

Quality of back vowels before /r/ in the American Inland North

Three American English diphthongs involving onsets in the back of the vowel space were investigated by means of acoustic measurements, discriminant analysis, and perceptual experiments. These diphthongs, termed DOOR/WAR, TOY, and STAR, were observed in the speech of ten young women residing in southern Michigan. The diphthongs were elicited in a variety of /b/-, /ɡ/-, and / h /-initial words (e.g. board , Boyd , and barred ). Words with similar consonantal margins but different nuclei (e.g. bode , baud , and bod ) were elicited, as well. The DOOR/WAR and TOY words were compared with bode and baud (and similar words with initial /ɡ/ and / h /), while the STAR words were compared with baud and bod (and similar words with initial /ɡ/ and / h /). All three methods of investigation showed that the initial part of the DOOR/WAR and TOY diphthongs more closely resembles that of bode than baud . On the other hand, the initial part of the STAR diphthong was shown to be intermediate between that of baud and that of bod .

Intelligibility of sinewave consonants

A good deal of experimental work has assessed the intelligibility of sinewave speech (SWS), synthesized by mixing sinusoids that follow the formants of natural utterances. While SWS is clearly intelligible at some level, most SWS work has been conducted using sentences, whose intelligibility is affected by many factors in addition to those related to recognition at the phonetic level. Earlier work [Hillenbrand et al., J. Acoust. Soc. Am, 129, 3991–4000] measuring the intelligibility of SWS vowels in isolated syllables reported an identification rate of 55%, far above chance but ~40 percentage points lower that of the original signals. The present work tested the intelligibility of SWS versions of 23 consonant types in CV and VCV syllables with three vowel types ([ɑ i u]) spoken by one man and one woman. SW signals were generated from unedited envelope peaks rather than formants. Intelligibility averaged across 59 listeners was 59%, with large variability across both listeners (sd = 9.9) and, especially, c...