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This dissertation focusses on the so-called "voicing effect", by which vowels tend to be shorter when followed by voiceless stops and to be longer when followed by voiced stops, as exemplified by the English word pair *bat* vs *bad*. While the presence of this effect is cross-linguistically widespread, less is known about the source(s) of this phenomenon and competing accounts have been proposed over the decades. In this work, I draw from acoustic and articulatory data of Italian, Polish, and English and offer an overarching account of which aspects of the production of voiceless vs voiced stops, and vowel/consonant sequences in general, contribute to the emergence of the voicing effect. The results indicate that the voicing effect is the product of a mechanism of compensation between the duration of the vowel and that of the following stop closure. The acoustic temporal relations of consonants and vowels observed in disyllabic (CV́CV) words of Italian, Polish, and English suggest that the duration of the interval between the release of the two stops is not affected by the voicing of the second stop. The release-to-release interval has similar duration in words with a voiceless C2 and those with a voiced C2. Within this temporally stable interval, the timing of the closure onset (the VC boundary) determines the duration of both the vowel and the stop closure. Ultrasound tongue imaging and electroglottographic data of Italian and Polish further show that the timing of the closure onset of voiced and voiced stops depends on articulatory factors related to the implementation of voicelessness and voicing. In particular, I argue that a delayed closure onset allows for enough tongue root advancement (known to facilitate voicing during closure) to be implemented during the production of the vowel in anticipation of the stop closure. Furthermore, glottal spreading typical of voiceless stops also can affect the timing of closure by anticipating the achievement of closure. These two factors, among other known factors, contribute to the observed pattern of short voiced closures and long preceding vowel duration, and, vice versa, long voiceless closures and short preceding vowel duration.

The human voice is the most common `carrier' of speech, but how does linguistic voice quality affect speech production and perception? Typical `modal' voice possesses a single fundamental frequency (f0), identified as the voice's pitch. Period doubling, known as a commonly-occurring type of creaky voice, consists of alternating glottal pulses with different periods and/or amplitudes for which multiple fundamental frequencies (f0s) co-exist. Thus, the pitch during period doubling is often indeterminate, and so it is unclear whether linguistic tone is identifiable, and how linguistic tone is identified, in this voice. Although period doubling has been mostly studied in voice disorders and singing styles, it frequently occurs in non-pathological voices, and its defining characteristics remain to be determined.This dissertation contributes three studies to characterize the physical, distributional, and perceptual aspects of period-doubled voice. Simultaneous electroglottography (EGG) and audio recordings of a Mandarin read speech corpus were analyzed to capture properties of the articulation and acoustics of period doubling in Chapters 2 and 3; artificial language learning and shadowing experimentation were used to probe perception of period doubling in Chapter 4.The EGG study in Chapter 2 finds that period doubling is articulated as two alternating pulses with distinct pitches as well as voice qualities. Specifically, I show that the glottal cycles in period doubling are not generally constricted, but instead oscillate between degrees of constriction shown by alternating contact quotients, pulse shape, and speed of vocal fold contact. This in addition to the alternating frequencies likely leads to the indeterminate pitch and quality percept in period doubling. The results also pose challenges to the existing taxonomy of creaky voice subtypes based on the established acoustic attributes.The acoustic analysis in Chapter 3 finds that period doubling is characterized acoustically via lower spectral tilt due to a stronger second harmonic from the original f0 (the first harmonics is derived from subharmonics), which distinguishes period doubling from vocal fry (another creaky-like voice quality) and modal voice. The results of the prosodic distribution show that, in Mandarin, period doubling occurs most frequently at the ends of utterances whereas vocal fry occurs at a post-focal position. This suggests that period doubling reflects vocal instability at the beginning and end of phonation, whereas vocal fry may be marking a weak prosodic element.The perception study in Chapter 4 finds that both Mandarin and English listeners hear a `low-tone' during period doubling, which is driven by the strength of frequency modulation more than that of amplitude modulation. When frequency modulation is at extremes, pitch is heard unambiguously as a lower tone. When frequency modulation is weak, pitch is often heard as ambiguous -- both high and low tones are possible. Further, listeners are able to imitate the period-doubled tones not only by adjusting f0, but by also modulating their voice quality. It is predicted that period doubling is used to signal low tones and could interfere with perception of tone of a high pitch.Together, this dissertation establishes period doubling not only as a phonetic category distinct from other voicing types such as modal voice and vocal fry, but also serves a distinct linguistic role based on its phonetic aspects and role in perception. The findings provide insight into speech production, perception, and processing, with implications for how period doubling can be synthesized and used to convey linguistic meaning.

This dissertation investigated aerodynamic, glottographic, and acoustic differences between habitual and clear speech. Nine normal-speaking individuals (five cis female, 4 cis male) were asked to read six short sentences in four reading conditions: habitual reading, habitual reading while holding a mask to the face to capture airflow and oral air pressure, clear reading, and clear reading while holding the mask to the face. Mask-off conditions in both habitual and clear reading manners were used for acoustic analyses, and mask-on conditions were used for aerodynamic and glottographic analyses. The instruction for eliciting habitual speech was “Read each sentence as if you are talking with a friend across the table.” The instruction for eliciting clear speech was “Read the sentences as clearly as possible by enunciating well, as if someone is having trouble understanding you.” Acoustic and time-related results indicated that from habitual to clear speech: (1) sentence duration increased, (2) speaking rate decreased, (3) duration of stressed vowels and unvoiced fricatives increased, (4) voice onset time increased for some unvoiced plosives, (5) stop gap duration increased, (6) fundamental frequency did not change except for two stressed vowels in female speakers for which fo increased, and (7) intensity of stressed vowels and stop consonants increased, but not for unvoiced fricatives (except for /ʃ/). Aerodynamic results indicated that from habitual to clear speech, there was greater (1) oral air pressure, (2) average airflow, (3) total air volume, and (4) peak flow during the release of the voiceless bilabial stop, suggesting the influence of greater subglottal pressure. In contrast, there was little to no change in glottal dynamics such as EGG width, EGG height, EGG contact and open quotients, and glottal airflow timing measures. In this study, it might be inferred that clear speech was a phenomenon that is more related to subglottal pressure and oral cavity kinematics than to vocal fold adduction and vibratory dynamics.

Objective:Art song is a unique genre in the realm of European classical music, which embraces the combined beauty of vocal melody, instrumental accompaniment, and text. In a performance context, the same composition can be performed with a variety of emotional interpretations. The purpose of this study was to determine sound production differences relative to two emotional interpretations in performing an excerpt from a classical art song. Methods/Design:The first author, a soprano with a master’s degree in vocal performance, recorded an excerpt from “La Mort d’Ophelie” composed by Hector Berlioz (1803-69). The excerpt was sung in two contrasting musical interpretations: an “empathetic legato” approach, and a “sarcastic” approach with emphatic attacks. Microphone, airflow (Glottal Enterprises MSIF-2), and electroglottography (EGG; Kay Model 6103) signals were digitized. These recordings were analyzed for acoustic, airflow, and glottographic measures. The vowels in the musical excerpt were analyzed in terms of intensity, long term average spectra (LTAS), fundamental frequency vibrato rate and extent, vowel onset, intensity comparison of harmonic frequencies, and glottal measures based on electroglottograph waveforms. Results & Conclusions:Data analyses revealed that stressed vowels, when performed with the emphatic approach compared to the legato approach, had faster vowel onset, increased glottal adduction (relative to the EGGW25 measure), increased intensity of harmonics in the 1500 to 3000 Hz range, inferred increase in subglottal pressure, increased airflow for the /f/ consonant, and greater aspiration airflow for the plosives /t/ and /p/. The vibrato extent for both fo and airflow were both greater for the emphatic approach. Findings also revealed larger amplitude values of the EGG waveform, but this finding was not statistically significant. Long-term average spectrum (LTAS) analyses of the entire production displayed minor increases across all formant frequencies for the emphatic approach. While this is a single-case objective study, it emphasizes the reality and informative nature of physiological, aerodynamic, and acoustic production differences in the pedagogical and interpretive aspects of art song performance. Vocal performers, teachers, and other music educators may benefit from applying findings like those of this study to developing performance strategies while maintaining healthy vocal production.

The current investigation aimed to compare four different measurement approaches for the determination of voice onset time for the six English stop consonants, where VOT is defined as the "burst to onset of phonation". The signals of interest were the wideband airflow, microphone, electroglottograph, and the spectrographic display. A primary question was whether the use of the wideband airflow signal results in shorter VOT measurements. Two adult males and two adult females produced "CV-the-CV" utterances (e.g.,"pa the pa") containing the six English stop consonants across two conditions, habitual vs. clear speech. Visual measurements were from the burst to the initial detection of phonation (IDP). The wideband airflow gave the shortest VOT measures. For habitual speech and for the voiceless stop consonants, the airflow signal revealed glottal airflow oscillations on average of 1.7 ms sooner than the microphone signal, 8.1 ms sooner than the EGG signal, and 13.6 ms sooner than spectrographic formant detection. The VOT differences between the airflow and microphone signals were not significant. For voiced stop consonants, the airflow signal typically also gave similar values of VOT as the microphone signal, and on average 6 ms sooner than the formant excitation and 5 ms sooner than the electroglottograph signal. The study emphasizes the finding that the initial detection of phonation often appears earlier after the consonant burst for the wideband airflow and microphone signals in comparison to the electroglottograph and spectrographic signals.

Although stress has been frequently attributed to voice disorder development and progression, little work has been done to determine the role of activation of the two major stress systems [the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis (HPA)] on changes in voice production parameters.Nineteen healthy female participants (median age: 18; range: 18 to 23) were subjected to the Trier Social Stress Test protocol. Voice production parameters (average airflow, estimated subglottal pressure, laryngeal airflow resistance, open quotient from the EGG signal, speaking fundamental frequency, and percent of syllables produced in vocal fry) were measured at seven measurement time points (2 before the stressor, 1 after an anticipatory period, and 4 after the stressor). Participants rated their levels of stress and nine emotions and provided saliva samples at each measurement time. Salivary cortisol and salivary alpha-amylase were measured from the saliva samples.Ten of the 19 participants experienced a minimum 2.5 nmol/l increase in salivary cortisol levels from before the stressor to after the stressor, indicating that they had HPA axis activation. There were no significant changes in aerodynamic or electroglottographic measures over the seven measurement time points. There was a significant increase in speaking fundamental frequency before the stressor and a reduction in fundamental frequency after the stressor. Estimated subglottal pressure and laryngeal airflow resistance measures were significantly higher in participants who did not experience an HPA axis response. The findings of the current study further support the body of literature that has reported mainly individual changes in voice production parameters following stress. However, the addition of salivary cortisol measures in the present study revealed the novel finding that there are consistent voice production differences between participants who experience HPA axis activation and those who do not. The higher estimated subglottal pressure and laryngeal airflow resistance measures in the group of participants who did not experience HPA activation overlap with pressures and resistances reported for those with voice disorders. Based on this, it is postulated that HPA axis response may be related, either through behavioral or physical adaptations, or personality factors, to the development of voice disorders.

As a singer, register transitions can be challenging to navigate. A singer must perceive where the transition is occurring and apply adjustments to smooth the transition. Within register transitions, one may experience various types of vocal instabilities. The primary aim of this research was to study the production mechanisms characterizing vocal instabilities in the untrained female singer. This was an exploratory study that included five untrained female singers who produced “normal” octave scales as well as scales as smoothly as they could. Simultaneous recordings of airflow, microphone, and EGG signals were analyzed. The scales were divided into three groups based on the perceptual consensus of level of smoothness. Unsteady scales contained aphonic segments, abrupt registration fluctuations, obvious intensity changes, and unexpected fundamental frequency (fo) variations. Subtler unsteady scales exhibited noticeable but “understated” quality changes, increased speed of fo changes or overshoots, and smaller yet evident intensity variations. The participants often produced perceivably smooth scales with minimal instability. Results suggest that untrained female singers are capable of producing perceptually smooth scales across register transitions. However, within some of these perceptually smooth scales, subtle changes and disturbances were noticed that result in the perception of minor instabilities. These subtleties are often seen more clearly within the airflow signal, EGG signal shifts, and fo rate of change than are aurally perceptible. For the unsteady scales, the more obvious instabilities were seen within nearly all measures, most notably in the airflow, fo, and intensity contours, and EGG waveform width and height. This study offers insights into a wider range of steadiness of vocal production where objective recordings reveal subtle changes that are difficult to hear.

Airflow vibrato is the fluctuation in average airflow while singing with vibrato. Understanding airflow vibrato relates to a deeper understanding of its importance to physiological, pedagogical, and clinical aspects. Two studies were performed to examine airflow vibrato. The subjects for Study 1 were four professional Western classical singers, and for Study 2 four highly trained amateur singers. Aerodynamic and acoustic measures were compared among vibrato, bleating (a primarily adductory gesture), and external epigastric pumping (EEP, a primarily subglottal pressure manipulation). Utterances included speaking (phonation and whisper) and singing (constant /a/ vowel, different pitches and loudness levels). Study 1 demonstrated how airflow vibrato compares with fundamental frequency (F0) and intensity vibrato. The correlation between rates of airflow and F0 vibrato was moderately strong. Mean airflow vibrato extents were larger for the female singers than for the male singers, and increased with pitch increase for all four singers. For the males, average airflow extent was 30 and 75 cm3/s for their lower and higher pitch, respectively, and for the females, 47 cm3/s and 94 cm3/s for their lower and higher pitch, respectively. Study 2 was undertaken to better understand sources of airflow vibrato. Airflow modulations were produced during singing with vibrato and also while bleating and with external epigastric pumping. Bleating had the fastest alteration rate (9.5-12 Hz), whereas the other types had similar rates (vibrato: 4.8-6.0 Hz; EEP: 6.0–7.5 Hz). During phonation (combining all conditions), bleating had the largest airflow modulation extents (on average 144 cm3/s, compared to 30 cm3/s for vibrato and 46 cm3/s for EEP).Overall results suggest that airflow vibrato typically leads F0 vibrato, and often has a more complex waveshape than F0 vibrato. Hypotheses generated from the study include: (1) A primarily subglottal pressure driven vibrato may provide relatively consistent but wide extents for both F0 and airflow vibrato. (2) A primarily glottal adduction driven vibrato may provide relatively low and inconsistent F0 vibrato extent, and high and inconsistent airflow extent. (3) A primarily CT driven vibrato may result in moderate to large F0 vibrato extent, and low airflow vibrato extent, with variable consistency.