Changes In Formant Frequencies Research Articles

Formant discrimination of speech and non-speech sounds for English and Chinese listeners

Thresholds of formant discrimination of speech and non-speech sounds were compared for native listeners of English and Chinese. English listeners showed significantly better thresholds than Chinese listeners, not only for English vowels, but also for Chinese vowels. Thresholds for vowel-spectrum-shaped noise were comparable for the two groups. These results suggest that English listeners are more sensitive to formant frequency changes of vowel stimuli than Chinese listeners, possibly due to the denser vowel space for English than for Mandarin Chinese. However, the psychophysical capacity to discriminate formant frequency changes in non-speech sounds is similar for English and Chinese listeners.

Comparative electromagnetic articulographic study of English rhythm as produced by native and non-native speakers

Previous work suggests that concurrent changes in jaw displacement and formant frequencies may manifest rhythm of spoken American English utterances [e.g., Erickson, in Proceedings of the Speech Prosody 2010, Chicago (May 2010), p. 1]. This paper compares jaw displacement and corresponding formant frequencies of monosyllabic American English words produced on low vowels in four word phrases with varying positions of emphasis as spoken by three native speakers and three Japanese speakers of English. Preliminary findings suggest an alternating pattern of strong-weak jaw displacement along with corresponding formant changes for the native speakers. This pattern was not consistently seen for the non-native speakers and seemed to vary as a function of their skill-level in spoken English.

Talker-to-listener distance effects on speech production and perception

Simulating talker-to-listener distance (TLD) in virtual audio environments requires mimicking natural changes in vocal effort. Studies have identified several acoustic parameters manipulated by talkers when varying vocal effort. However, no systematic study has investigated vocal effort variations due to TLD, under natural conditions, and their perceptual consequences. This work examined the feasibility of varying the vocal effort cues for TLD in synthesized speech and real speech by (a) recording and analyzing single word tokens spoken at 1 m < or = TLD < or = 32 m, (b) creating synthetic and modified speech tokens that vary in one or more acoustic parameters associated with vocal effort, and (c) conducting perceptual tests on the reference, synthetic, and modified tokens to identify salient cues for TLD perception. Measured changes in fundamental frequency, intensity, and formant frequencies of the reference tokens across TLD were similar to other reports in the literature. Perceptual experiments that asked listeners to estimate TLD showed that TLD estimation is most accurate with real speech; however, large standard deviations in the responses suggest that reliable judgments can only be made for gross changes in TLD.

Improvement of vowel formant discrimination: Effects of global and local enhancement.

Vowel formant discrimination measures the smallest change in vowel formant frequency that is detectable. Thresholds of vowel formant discrimination were examined for F2 frequency of three American English vowels on normal-hearing and hearing-impaired listeners. Vowel stimuli were manipulated with a global enhancement by increasing speech level from 70- to 90-dB SPL and a local enhancement by increasing F2 amplitudes of 3, 6, and 9 dB. For each listener, vowel formant discrimination was tested for six sets of stimuli (3 local F2 enhancement × 2 global enhancement). Results showed that both normal-hearing and hearing-impaired listeners significantly benefited from local enhancement and local plus global enhancement, but not from global enhancement only. In addition, the improvement in vowel formant discrimination for hearing-impaired listeners was substantially higher than for normal-hearing listeners. However, given the same formant structure (original or enhanced F2), normal-hearing listeners did not receive any benefit from increasing the global level from 70- to 90-dB SPL. On the other hand, hearing-impaired listeners improved their thresholds from 70- to 90-dB SPL, but only when enhanced F2 was presented. There results indicate that, to improve vowel formant discrimination, local enhancement of target formant amplitude is more important than global enhancement.

Dialectal differences in dynamic formant patterns in vowels.

This study examines basic acoustic variation in the dynamic patterns of vowel formants among three regional variants of American English spoken in southeastern Wisconsin (affected by the Northern Cities Shift), western North Carolina (Appalachian English affected by the Southern Vowel Shift), and central Ohio (not considered to be affected currently by any vowel shift). Three groups of speakers (including men and women) produced vowels in citation form (in a /hVd/ context) and in sentences. The sentence material elicited two degrees of vowel emphasis (high and low) in the /bVd/ and /bVt/ contexts. The frequencies and amplitudes of the first three formants were extracted at points corresponding to 20%‐35%‐50%‐65%‐80% of the vowel’s duration. A set of dynamic measures was then calculated using these values that included overall signed/unsigned change in formant frequencies, vector and trajectory lengths, direction/angle of vowel movement in the F1 by F2 plane, and rate of frequency change. The results show significant cross‐dialectal differences in formant patterns in monophthongs, phonemic diphthongs, and nonphonemic diphthongs. The nature and extent of these formant changes varied as a function of speaker dialect in a manner apart from expected variation resulting from phonetic and prosodic context and speaking style. [Work supported by NIH.]

Cross-modal synchrony perception reveals aspects of categorical perception

The phenomenon of "categorical perception" has played an important role in speech research. When a specific (combination of) feature(s) of a speech stimulus is varied along a physical dimension, categorical perception is reflected by two observations: (1) the percept of the sound changes abruptly from one category to another, e.g., from "ba" to "da" to "ga" for changes in formant transition frequencies, and (2) physical changes of a given amount lead to more easily perceivable differences for stimuli close to a category boundary, compared to stimuli in the center of a category. In this talk, I present data about audio-visual synchrony perception, which indicate that perceived synchrony also reveals properties of categorical perception. Depending on the physical delay between the auditory and visual component, the percept changes from "audio first," to "synchronous" to "video first." When measuring sensitivity to changes in audio-visual delays, we observe that the thresholds are small for stimuli at the transitions between the earlier determined categories, while they are larger for stimuli within a category.

Der Einfluss von Cochlearimplantaten auf die Artikulation von Vokalen

Speech of deaf persons differs considerably from that of speakers with normal hearing. The purpose of this study was to investigate the acoustic changes in articulation of corner vowels in deaf children and adults after cochlear implantation. Thirteen prelingually deaf children and 12 postlingually deaf adults were included in the study. Voice samples of the isolated corner vowels /a/, /i/ and /u/ were analyzed before and 6-12 months after the implantation. The frequencies of the first (F1) and second (F2) formants, the F1/F2 ratio of all three corner vowels, and the area of the vowel triangle were calculated and compared before and 6-12 months after the implantation. In the adults, no significant differences were detected in the formant frequencies, the F1/F2 ratio or the area of the vowel triangle. However, significant change in formant frequencies was detected in the group of 13 prelingually deaf children. After the implantation the F1 of /u/ decreased significantly, and favorable decreases of the F1 of /i/ and the F1/F2 ratio in /i/ and /u/ were close to being statistically significant. All changes caused better phonological difference between the two vowels. The significant change in the F1 of /u/ and the change of F1 of /i/ resulted in the expansion of the vowel space, which was expressed as an increase in the area of the vowel triangle. We suggest that in children the acquired hearing ability and further development of neuromuscular control of articulation are the reasons for the significant improvement after cochlear implantation. The results also suggest that the area of the vowel triangle is a useful and sensitive indicator of the more precise articulation after implantation. In order to achieve better and faster improvement of articulation, regular speech therapy should be included in the rehabilitation of deaf persons after cochlear implantation.

Formant Characteristics of Vowels Produced by Mandarin Esophageal Speakers

With the use of the pharyngoesophageal (PE) segment as the neoglottis in esophageal speakers, their voice quality becomes significantly different from that of laryngeal speakers. The present study investigated the characteristics of the vocal tract resonance in Mandarin esophageal speakers. The first three formant frequencies of vowels /a, epsilon, i, [see in text], u, y/ produced by seven superior esophageal and seven laryngeal speakers of Mandarin were obtained. For each formant, the formant frequencies measured from the medial 80% of the vowel portion were averaged, and data obtained from esophageal speakers were compared with that obtained from laryngeal speakers. The results indicated that esophageal speakers were associated with significantly higher formant frequencies (F(1), F(2), and F(3)) and a significantly diminished vowel space circumscribed by the three corner vowels /i/, /a/, and /u/ when compared with laryngeal speakers. The findings that formant frequency changes across vowels were systematic and similar for esophageal and laryngeal speakers are consistent with those previously reported in English. It can be concluded that vocal tract transmission has been changed in esophageal speakers of Mandarin after laryngectomy.

Testing theories of vowel inherent spectral change

Three competing accounts of vowel inherent spectral change in English all agree on the importance of initial formant frequencies; however, they disagree about the nature of the perceptually relevant aspects of formant change. The onset+offset hypothesis claims that the final formant values themselves matter. The onset+slope hypothesis claims that only the rate of change counts. The onset+direction hypothesis claims that only the general direction of change in formant frequencies is important. A synthetic-vowel perception experiment was designed to differentiate among the three. Results provide support for the superiority of the onset+offset hypothesis.

Vocal tract length perturbation and its application to male-female vocal tract shape conversion

An alternative and complete derivation of the vocal tract length sensitivity function, which is an equation for finding a change in formant frequency due to perturbation of the vocal tract length [Fant, Quarterly Progress and Status Rep. No. 4, Speech Transmission Laboratory, Kungliga Teknisha Hogskolan, Stockholm, 1975, pp. 1-14] is presented. It is based on the adiabatic invariance of the vocal tract as an acoustic resonator and on the radiation pressure on the wall and at the exit of the vocal tract. An algorithm for tuning the vocal tract shape to match the formant frequencies to target values, such as those of a recorded speech signal, which was proposed in Story [J. Acoust. Soc. Am. 119, 715-718 (2006)], is extended so that the vocal tract length can also be changed. Numerical simulation of this extended algorithm shows that it can successfully convert between the vocal tract shapes of a male and a female for each of five Japanese vowels.

The influence of creaky voice on formant frequency changes

When disguising their voice, women may tend to lower their fundamental frequency so as to imitate a male’s voice. This implies a lowered fundamental frequency on the one hand and the production of creaky voice or creak over large sequences on the other. For speaker identification which additionally relies on formant frequency comparison, it is therefore of interest if the production of creaky voice implies an additional modification of the vocal tract and consequently has an effect on formant frequencies. In the present study, the second and third formant of 750 creaky and modal vowels of five female and four male speakers were compared. As a main result, a sex-specific difference has been observed. Creaky vowels produced by women show a lower second formant as compared to the same vowels produced by the same speaker using modal phonation. Changes in the third formant during low creaky voice disguise by women and, more generally, the effect on male formant values, was found to be inconsistent.

Changes in formant frequencies associated with postural change in adult male speakers over 50 years old

It is possible that changes of direction of gravity relative to the vocal tract associated with changes in posture influence acoustic characteristics of speech including vowel formant frequencies. Studies examining such effects had produced mixed results and demonstrated the possibility of substantive interspeaker variability in the effect of postural changes on vowel formant frequencies. Recent work by Takakura et al. [‘‘Changes in formant frequencies associated with postural change,’’ paper presented at the Fall meeting of Acoustical Society of Japan (2006)], using young adult male speakers, revealed a small number of speakers demonstrating changes in vowel formant frequencies and suggested effect of age. The present study attempts to examine changes of vowel formant frequencies in upright and supine position among older male speakers. Attempts will be made to eliminate the effect of differences in neck position between the postures through the use of a power-bead-based neck stabilizer. The results will be compared with data from young normal speakers in the previous study and inferences will be made relative to speech production models.

Rhesus macaques spontaneously perceive formants in conspecific vocalizations

We provide a direct demonstration that nonhuman primates spontaneously perceive changes in formant frequencies in their own species-typical vocalizations, without training or reinforcement. Formants are vocal tract resonances leading to distinctive spectral prominences in the vocal signal, and provide the acoustic determinant of many key phonetic distinctions in human languages. We developed algorithms for manipulating formants in rhesus macaque calls. Using the resulting computer-manipulated calls in a habituation/dishabituation paradigm, with blind video scoring, we show that rhesus macaques spontaneously respond to a change in formant frequencies within the normal macaque vocal range. Lack of dishabituation to a "synthetic replica" signal demonstrates that dishabituation was not due to an artificial quality of synthetic calls, but to the formant shift itself. These results indicate that formant perception, a significant component of human voice and speech perception, is a perceptual ability shared with other primates.

Vowel production with and without auditory feedback in children with cochlear implants

The effects of auditory feedback on vowel formant frequencies were investigated in the speech produced by three early-implanted (received cochlear implants before the age of 3 years) and three late-implanted children (after 5 years). The syllables /heed/, /hid/, /had/, /whod/, /hood/, and /hod/ were produced in a carrier sentence 12 times, each in both implant processor ON (auditory feedback present) and OFF (feedback absent) conditions. Comparisons of the vowel formant frequencies in processor ON versus OFF conditions revealed primarily second formant frequency (F2) shifts for a majority of the vowels, while showing minimal changes in the first formant frequencies (F1). In addition, a majority of the F2 shifts was towards the middle of the vowel space, suggesting centralization of vowels in the absence of auditory feedback. Further, most of the formant frequency changes were present in the vowels produced by late- compared to early-implanted children. These findings suggest that the late-implanted children may rely on auditory feedback to a greater extent than early-implanted children for speech production. Implications of the short-term effects of auditory feedback on speech production will be discussed in reference to the feedback and feed-forward models for speech production. [Work supported by NIH/NIDCD R03DC007052-01.]

A comparison of vowel formant frequencies in the babbling of infants exposed to Canadian English and Canadian French

It is well established that normally developing infants typically enter the canonical babbling stage of production between 6 and 8 months of age. However, whether the linguistic environment affects babbling, either in terms of the phonetic inventory of vowels produced by infants [Oller &amp; Eiler (1982)] or the acoustics of vowel formants [Boysson-Bardies et al. (1989)] is controversial. The spontaneous speech of 42 Canadian English- and Canadian French-learning infants aged 8 to 11, 12 to 15 and 16 to 18 months of age was recorded and digitized to yield a total of 1253 vowels that were spectrally analyzed and statistically compared for differences in first and second formant frequencies. Language-specific influences on vowel acoustics were hypothesized. Preliminary results reveal changes in formant frequencies as a function of age and language background. There is evidence of decreases over age in the F1 values of French but not English infants vowels, and decreases over age in the F2 values of English but not French infants vowels. The notion of an age-related shift in infants attention to language-specific acoustic features and the implications of this for early vocal development as well as for the production of Canadian English and Canadian French vowels will be discussed.

Formant detail needed for vowel identification

Changes in formant frequency over time are important for vowel identification: listeners identify stimuli containing time-varying formants better than stimuli with steady-state formants. Statistically based pattern classifiers used as models for human perception have shown that very coarse representations of formant change over time result in accurate classification of American English vowels. In this study, using synthetic stimuli with five levels of formant contour detail, human listeners achieved maximum vowel identification for relatively coarse representations of formant movement containing information about onset, offset, and midpoint frequencies. More detailed representations of contour did not improve identification for most vowels.

Intracortical responses in human and monkey primary auditory cortex support a temporal processing mechanism for encoding of the voice onset time phonetic parameter.

This study tests the hypothesis that temporal response patterns in primary auditory cortex are potentially relevant for voice onset time (VOT) encoding in two related experiments. The first experiment investigates whether temporal responses reflecting VOT are modulated in a way that can account for boundary shifts that occur with changes in first formant (F1) frequency, and by extension, consonant place of articulation. Evoked potentials recorded from Heschl's gyrus in a patient undergoing epilepsy surgery evaluation are examined. Representation of VOT varies in a manner that reflects the spectral composition of the syllables and the underlying tonotopic organization. Activity patterns averaged across extended regions of Heschl's gyrus parallel changes in the subject's perceptual boundaries. The second experiment investigates whether the physiological boundary for detecting the sequence of two acoustic elements parallels the psychoacoustic result of approximately 20 ms. Population responses evoked by two-tone complexes with variable tone onset times (TOTs) in primary auditory cortex of the monkey are examined. Onset responses evoked by both the first and second tones are detected at a TOT separation as short as 20 ms. Overall, parallels between perceptual and physiological results support the relevance of a population-based temporal processing mechanism for VOT encoding.

Mismatch negativity to frequency changes: no evidence from human event-related brain potentials for categorical speech processing of complex tones resembling vowel formant structure

Based on a memory-comparison process, changes in the pitch of repetitive sounds are pre-attentively detected, reflected by the mismatch negativity (MMN) event-related brain potential. In the present investigation of categorical speech perception, complex tones were used that consisted of vowel-defining F1 and F2 formant information while not being perceived as speech. MMN was obtained in oddball blocks. The auditory system tracks two simultaneous changes in formant frequencies of 50 Hz while also abstracting from three levels of intensity variation. Lower frequency deviants elicited larger MMN. No effects of language-categorical processing were observed.

Mismatch negativity to frequency changes: no evidence from human event-related brain potentials for categorical speech processing of complex tones resembling vowel formant structure

Based on a memory-comparison process, changes in the pitch of repetitive sounds are pre-attentively detected, reflected by the mismatch negativity (MMN) event-related brain potential. In the present investigation of categorical speech perception, complex tones were used that consisted of vowel-defining F1 and F2 formant information while not being perceived as speech. MMN was obtained in oddball blocks. The auditory system tracks two simultaneous changes in formant frequencies of 50 Hz while also abstracting from three levels of intensity variation. Lower frequency deviants elicited larger MMN. No effects of language-categorical processing were observed.

The influence of creaky voice on formant frequency changes

When disguising their voice, women may tend to lower their fundamental frequency so as to imitate a male’s voice. This implies a lowered fundamental frequency on the one hand and the production of creaky voice or creak over large sequences on the other. For speaker identification which additionally relies on formant frequency comparison, it is therefore of interest if the production of creaky voice implies an additional modification of the vocal tract and consequently has an effect on formant frequencies. In the present study, the second and third formant of 750 creaky and modal vowels of five female and four male speakers were compared. As a main result, a sex-specific difference has been observed. Creaky vowels produced by women show a lower second formant as compared to the same vowels produced by the same speaker using modal phonation. Changes in the third formant during low creaky voice disguise by women and, more generally, the effect on male formant values, was found to be inconsistent.