Boundary accents/tones

The AM school (which includes ToBI) describes intonation in terms of abstract High and Low tones. Diacritics (, %, -) are used to specify which tones align with syllables and boundaries. The tones can be combined in various ways to form an inventory of pitch accents (e.g. H +L). 

Figure 6.1 Example of FO contour with pitch accents and boundary tones maiked.

Beyond this, we again find that there is httle agreement about how to describe pitch accents and boundary tones. Some theories state there are a fixed inventory of these, while some describe them with continuous parameters. The nature of pitch accents and boundary tones is disputed, with some theories describing them as tones or levels while others say their characteristic properly is pitch movement. One prominent theory states that we have an intonational phonology that parallels normal phonology, and as such we have inventories of contrasting units (sometimes called... 

Of all the prosodic phenomena we have examined intonational tune is the most heavily related to augmentative and particularly affective content. In situations where these effects are absent, we can say to a first approximation that all utterances have in fact the same intonational tune the only differences occur as to where the pitch accents and boundary tones which make up this tune are positioned. Hence we can almost argue that for discourse neutral synthesis, there simply isn t any intonational tune prediction to be done. In other words, the real task is to predict a suitable FO contour that e q)resses the prominence and phrasing patterns and encodes the suprasegmental, rather than true prosodic patterns of the utteranee. 

The other main area of interest in tune description concerns what happens at the ends of intonation phrases. Often FO is low at a phrase boundary, but in many circumstances FO is high. For instance, if another phrase directly follows the current one, a continuation rise may be present. If the tune is that of a yes/no question, the final pitch may also be high. The British school deals with these effects by using different nuclear accent and tail configurations. The AM model makes use of high and low boundary tones which distinguish the different types of contour. 

Unlike the British school analysis, there is no strict division of the contour into regions such as head and nucleus. Both nuclear and pre-nuclear accents can be any one of the six types described above. The nucleus accent is distinguished because the phrase and boundary tones that follow it allow a much larger inventory of intonational effects. 

One solution that is increasingly adopted is to forgo the distinction between label types altogether, see for instance [488]. While the break index and boundary tone components are often kept, only a single type of pitch accent is used in effect the labellers are marking whether a word is intonationally prominent or not. However, it should be clear that such an approach effectively reduces ToBI to a data driven system of the type described below. 

The other major intonational effect is the behaviour at phrase boundaries. The FO at these points can be systematically raised or lowered for specific effect. The term boundary tone is often used as the equivalent intonation imit to pitch accent. Strictly speaking, this term is applicable only to AM models, but it has gained wide enough usage that we use it here to describe general behaviour at boimdaries regardless of whether the particular model uses tones or not. 

In the Tilt model, there are two types of event, accent and boundary (fliese are effectively the same as the pitch accents and boundary tones in the AM model). Each event comprises two parts, a rise and a fall, as shown in Figure 9.12. Between events straight lines called connections are used. All variation in accent and boundary shape is governed firstly by the relative sizes of the rise and fall components and secondly by how the event aligns with the verbal component (basically whether it is higher or... 

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