Speech rate has been shown to vary across social categories such as gender, age, and dialect, while also being conditioned by properties of speech planning. The effect of utterance length, where speech rate is faster and less variable for longer utterances, has also been shown to reduce the role of social factors once it has been accounted for, leaving unclear the relationship between social factors and speech production in conditioning speech rate. Through modelling of speech rate across 13 English speech corpora, it is found that utterance length has the largest effect on speech rate, though this effect itself varies little across corpora and speakers. While age and gender also modulate speech rate, their effects are much smaller in magnitude. These findings suggest utterance length effects may be conditioned by articulatory and perceptual constraints, and that social influences on speech rate should be interpreted in the broader context of how speech rate variation is structured.

The relationship between prosodic structure and segmental realisation is a central question within phonetics. For vowels, this has been typically examined in terms of duration, leaving largely unanswered how prosodic boundaries influence spectral realisation. This study examines the influence of prosodic boundary strength-as well as duration and pauses-on vowel dynamics in spontaneous Japanese. While boundary strength has a marginal effect on dynamics, increased duration and pauses result in greater vowel peripherality and spectral change. These findings highlight the complex relationship between prosodic and segmental structure, and illustrate the importance of multifactorial analysis in corpus research.

Vowels are typically characterized in terms of their static position in formant space, though vowels have also been long-known to undergo dynamic formant change over their timecourse. Recent studies have demonstrated that this change is highly informative for distinguishing vowels within a system, as well as providing additional resolution in characterizing differences between dialects. It remains unclear, however, how both static and dynamic representations capture the main dimensions of vowel variation across a large number of dialects. This study examines the role of static, dynamic, and duration information for 5 vowels across 21 British and North American English dialects, and observes that vowels exhibit highly structured variation across dialects, with dialects displaying similar patterns within a given vowel, broadly corresponding to a spectrum between traditional 'monophthong' and 'diphthong' characterizations. These findings highlight the importance of dynamic and duration information in capturing how vowels can systematically vary across a large number of dialects, and provide the first large-scale description of formant dynamics across many dialects of a single language.

Recent advances in access to spoken-language corpora and development of speech processing tools have made possible the performance of "large-scale" phonetic and sociolinguistic research. This study illustrates the usefulness of such a large-scale approach-using data from multiple corpora across a range of English dialects, collected, and analyzed with the SPADE project-to examine how the pre-consonantal Voicing Effect (longer vowels before voiced than voiceless obstruents, in e.g., bead vs. beat) is realized in spontaneous speech, and varies across dialects and individual speakers. Compared with previous reports of controlled laboratory speech, the Voicing Effect was found to be substantially smaller in spontaneous speech, but still influenced by the expected range of phonetic factors. Dialects of English differed substantially from each other in the size of the Voicing Effect, whilst individual speakers varied little relative to their particular dialect. This study demonstrates the value of large-scale phonetic research as a means of developing our understanding of the structure of speech variability, and illustrates how large-scale studies, such as those carried out within SPADE, can be applied to other questions in phonetic and sociolinguistic research.

A number of recent studies have observed that phonetic variability is constrained across speakers, where speakers exhibit limited variation in the signalling of phonological contrasts in spite of overall differences between speakers. This previous work focused predominantly on controlled laboratory speech and on contrasts in English and German, leaving unclear how such speaker variability is structured in spontaneous speech and in phonological contrasts that make substantial use of more than one acoustic cue. This study attempts to both address these empirical gaps and expand the empirical scope of research investigating structured variability by examining how speakers vary in the use of positive voice onset time and voicing during closure in marking the stop voicing contrast in Japanese spontaneous speech. Strong covarying relationships within each cue across speakers are observed, while between-cue relationships across speakers are much weaker, suggesting that structured variability is constrained by the language-specific phonetic implementation of linguistic contrasts.

A central question in the Japanese high vowel devoicing literature concerns whether vowels are devoiced through a categorical process or via gradient reduction. Examining how vowel height and consonantal voicing condition phrase-internal CV duration in a corpus of spontaneous Tokyo Japanese, it was found that CVs containing high vowels are substantially shorter before voiceless consonants, whilst non-high vowels do not exhibit comparable shortening. This quantitative difference between CV durations suggests a controlled temporal compression of the CV, consistent with views that Japanese vowel devoicing is produced through a categorical process targeting high vowels preceding voiceless consonants, and supports previous observations made of elicited productions.

The ‘voicing effect’ – the durational difference in vowels preceding voiced and voiceless consonants – is a well-documented phenomenon in English, where it plays a key role in the production and perception of the English final voicing contrast. Despite this supposed importance, little is known as to how robust this effect is in spontaneous connected speech, which is itself subject to a range of linguistic factors. Similarly, little attention has focused on variability in the voicing effect across dialects of English, bar analysis of specific varieties. Our findings show that the voicing of the following consonant exhibits a weaker-than-expected effect in spontaneous speech, interacting with manner, vowel height, speech rate, and word frequency. English dialects appear to demonstrate a continuum of potential voicing effect sizes, where varieties with dialect-specific phonological rules exhibit the most extreme values. The results suggest that the voicing effect in English is both substantially weaker than previously assumed in spontaneous connected speech, and subject to a wide range of dialectal variability.

Many phonological processes can be affected by segmental context spanning word boundaries, which often lead to variable outcomes. This paper tests the idea that some of this variability can be explained by reference to production planning. We examine coronal stop deletion (CSD), a variable process conditioned by preceding and upcoming phonological context, in a corpus of spontaneous British English speech, as a means of investigating a number of variables associated with planning: Prosodic boundary strength, word frequency, conditional probability of the following word, and speech rate. From the perspective of production planning, (1) prosodic boundaries should affect deletion rate independently of following context; (2) given the locality of production planning, the effect of the following context should decrease at stronger prosodic boundaries; and (3) other factors affecting planning scope should modulate the effect of upcoming phonological material above and beyond the modulating effect of prosodic boundaries. We build a statistical model of CSD realization, using pause length as a quantitative proxy for boundary strength, and find support for these predictions. These findings are compatible with the hypothesis that the locality of production planning constrains variability in speech production, and have practical implications for work on CSD and other variable processes.