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Superficially, read and spontaneous speech—the two main kinds of training data for automatic speech recognition—appear as complementary, but are equal: pairs of texts and acoustic signals. Yet, spontaneous speech is typically harder for recognition. This is usually explained by different kinds of variation and noise, but there is a more fundamental deviation at play: for read speech, the audio signal is produced by recitation of the given text, whereas in spontaneous speech, the text is transcribed from a given signal. In this review, we embrace this difference by presenting a first introduction of causal reasoning into automatic speech recognition, and describing causality as a tool to study speaking styles and training data. After breaking down the data generation processes of read and spontaneous speech and analysing the domain from a causal perspective, we highlight how data generation by annotation must affect the interpretation of inference and performance. Our work discusses how various results from the causality literature regarding the impact of the direction of data generation mechanisms on learning and prediction apply to speech data. Finally, we argue how a causal perspective can support the understanding of models in speech processing regarding their behaviour, capabilities, and limitations. [ABSTRACT FROM AUTHOR]

Pluricentric languages are languages that are spoken in at least two countries where they have an official function and thus develop national varieties with specific linguistic and pragmatic features. Presently 43 languages have been identified as belonging to this category, for instance, English, Spanish, German, Bengali, Hindi and Urdu. This article forms an introduction to the special issue "Pluricentric Languages in Speech Science and Technology" by giving an overview of current challenges with respect to the development of speech and language resources, annotation and analysis tools, as well as speech technology services for pluricentric languages. The article discusses potential solutions that come from cross-fertilization: on the one hand, how phonetic and linguistic knowledge may contribute to advancements in speech technology, and on the other, how speech technology may facilitate phonetic and linguistic studies on pluricentric languages. In our discussion, we include the research methods and findings of the eight research articles of this special issue and point towards promising paths for future research in the field. [ABSTRACT FROM AUTHOR]

Chichimec (Otomanguean) has two tones, high and low, and a phonological three-way phonation contrast: modal /V/, breathy / V ¨ /, and creaky / V ̃ /. Tone and phonation type contrasts are used independently. This paper investigates the acoustic realization of modal, breathy, and creaky vowels; the timing of phonation in non-modal vowels; and the production of tone in combination with different phonation types. The results of cepstral peak prominence and three spectral tilt measures showed that phonation type contrasts are not distinguished by the same acoustic measures for women and men. In line with expectations for laryngeally complex languages, phonetic modal and non-modal phonation are sequenced in phonological breathy and creaky vowels. With respect to the timing pattern, however, the results show that non-modal phonation is not, as previously reported, mainly located in the middle of the vowel. Non-modal phonation is, instead, predominantly realized in the second half of phonological breathy and creaky vowels. Tone is distinguished in all three phonation types, and non-modal vowels do not exhibit distinct F0 ranges except for creaky vowels produced by women in which F0 declines in the creaky portion. The results of the acoustic analysis provide additional insights to phonological accounts of laryngeal complexity in Chichimec. [ABSTRACT FROM AUTHOR]

This paper investigates the nature of reduction phenomena in informal speech. It addresses the question whether reduction processes that affect many word types, but only if they occur in connected informal speech, may be categorical in nature. The focus is on reduction of schwa in the prefixes and on word-final /t/ in Dutch past participles. More than 2000 tokens of past participles from the Ernestus Corpus of Spontaneous Dutch and the Spoken Dutch Corpus (both from the interview and read speech component) were transcribed automatically. The results demonstrate that the presence and duration of /t/ are affected by approximately the same phonetic variables, indicating that the absence of /t/ is the extreme result of shortening, and thus results from a gradient reduction process. Also for schwa, the data show that mainly phonetic variables influence its reduction but its presence is affected by different and more variables than its duration, which suggests that the absence of schwa may result from gradient as well as categorical processes. These conclusions are supported by the distributions of the segments' durations. These findings provide evidence that reduction phenomena which affect many words in informal conversations may also result from categorical reduction processes. [ABSTRACT FROM AUTHOR]

Acoustic metrics of contrastive speech rhythm, based on vocalic and intervocalic interval durations, are intended to capture stable typological differences between languages. They should consequently be robust to variation between speakers, sentence materials, and measurers. This paper assesses the impact of these sources of variation on the metrics %V (proportion of utterance comprised of vocalic intervals), VarcoV (rate-normalized standard deviation of vocalic interval duration), and nPVI-V (a measure of the durational variability between successive pairs of vocalic intervals). Five measurers analyzed the same corpus of speech: five sentences read by six speakers of Standard Southern British English. Differences between sentences were responsible for the greatest variation in rhythm scores. Inter-speaker differences were also a source of significant variability. However, there was relatively little variation due to segmentation differences between measurers following an agreed protocol. An automated phone alignment process was also used: Rhythm scores thus derived showed good agreement with the human measurers. A number of recommendations for researchers wishing to exploit contrastive rhythm metrics are offered in conclusion. [ABSTRACT FROM AUTHOR]