ToBI (Tones and break indices) is a set of conventions for transcribing and annotating the prosody of speech. 'ToBI' is sometimes used to refer to the conventions used for describing English specifically, but ToBI systems have been defined for a number of other languages, for example J-ToBI refers to the ToBI conventions for Tokyo Japanese.
A ToBI transcription minimally indicates the intended prosodic grouping of an utterance and its tonal events.
For example, the sentence "Mary went to the store to get some milk" may be produced with a slight break after 'store', indicating that this sentence consists of two smaller units: "(Mary went to the store) | (to get some milk)". The English ToBI standard distinguishes four levels of boundary strength, corresponding roughly to breaks between constituents at different levels of the Prosodic Hierarchy. One signal of boundary strength is lengthening of the preceding syllable: the stronger the boundary, the more lengthening of the preceding syllable.
'Tonal events' include both pitch accents and boundary tones. Pitch accents, written as combinations of H and L tones (high and low, respectively), are typically realized on words that carry the most information in a sentence. For example, in the sentence "Mary went to the store to get some milk", a natural pronunciation would include pitch accents on 'Mary', 'store', and 'milk'. Boundary tones, also written with H and L, are affiliated not to words but to phrase edges. For example, the sentence "Mary went to the store" can be pronounced as a statement or a question ("Mary went to the store." vs. "Mary went to the store?") The contrast between the statement and the question is signalled by a boundary tone at the end of the phrase: a low boundary tone causes a falling pitch contour, signalling the statement, whereas a high boundary tone causes a rising pitch contour, signalling the question.
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