3.2 Labeling Methods
3.2.3 GToBI
GToBI stands for German ToBI and was developed in cooperation by Martine Grice, Matthias Reyelt, Ralf Benzmüller, Anton Batliner and Jörg Mayer (Grice et al., 1996). The labeling system has recently been modified in order to make it phonetically more transparent and to integrate recent advances in intonational phonology (Baumann et al., 2001). Grice et al. (to appear) presents a review of accounts for German intonation and a motivation for the GToBI model. In the fol-lowing the individual pitch accents and boundary tones are listed with a detailed description from the GToBI labeling guide. GToBI has two monotonal pitch ac-cents (Grice & Benzmüller, 1997):
H* The accent forms the peak of a more flat increase. There is no low or high target before the accented syllable. It is the default accent that is used when there are no clear indications for other accents. (see two examples in figure 4.1 in the following chapter); the so called ‘peak
Chapter 3. Literature Review 3.2 Labeling Methods accent’ is characterized by an upward movement of the pitch. The accented syllable sounds high. The upward movement is not as high as in the L+H* case.
L* ‘Low accent’ an apparent tone target on the accented syllable low in the speaker’s range, often corresponding to a dip in F0; characterized by a downward movement of the pitch or a low register. Usually the minimum of the pitch movement lies approximately in the middle of the vowel within the accented syllable.
There are four bitonal pitch accents proposed by GToBI:
L*+H A minimum is reached on the accented syllable. There will be an increase late in the accented syllable that ends in the following syllable (sometimes later). The accented syllable sounds low.
L+H* This pitch accent is characterized with a steep increase on the accented syllable. The endpoint of the increase is late in the accented syllable sometimes afterwards. Important is that the accented syllable sounds high. Important as well is that the syllable before the accent reaches a low target (see an example in figure 4.2 in the next chapter).
H+L* The accented syllable is low. The preceding one is high. The impres-sion of a large pitch jump towards a low level appears.
H+!H* Here a fall on the accented syllable from a high to a mid level of the speakers range occurs. The syllable preceding is higher. If H+!H* is followed by a L- boundary tone then the pitch decreases further. If it is followed by a H- pitch then it stays on the level of the !H*.
The above mentioned pitch accents may be labeled with an additional diacritic sig-naling “upstep” or “downstep” of the tones. Downstep is a lowering of an assumed topline of pitch range which shifts the F0 of an H accent downwards and is marked by placing a “!” symbol in front of the affected H tone. Upstep is used to indi-cate a step up within a sequence of pitch accents and also describes a step up to a boundary tone. Each accent of such a sequence is marked with a “^” symbol.
There are altogether four intonation phrase boundary tones and two intermediate phrase boundary tones proposed by GToBI. Boundary tones have to appear at the end of a phrase and may also appear at the beginning of phrases although the latter is usually unmarked. Two types of phrases are separated:
• intermediate phrase = ip = small boundary,
• intonation phrase = IP = large boundary.
3.2 Labeling Methods Chapter 3. Literature Review An intonation phrase consists of minimally one intermediate phrase and includes therefore always two boundary tones.
Boundary tones determine the course of intonation between the last accent (nuclear accent) and the end of a phrase. Boundary tones are labeled at the end of the last word in the phrase. This does often not correspond to the pitch contour and is just a convention. The two phrase accents are:
L- Phrase accent occurs at the end of an intermediate phrase. L- describes two parts of the pitch movement after the accent: (i) after H*, L+H*, H+!H*, L*+H a decrease in to the lower range of the speakers voice will be immediately following the accented syllable, (ii) the continued decrease of the contour towards the low baseline, that mostly ends on a following stressed (but not accented) syllable.
H- Phrase accent occurs at the end of an intermediate phrase. H- after H*, L+H*, H+!H* is realized with a continuation intonation. The pitch stays on the level of the H accent tone (or !H tone) or slightly above; it might also decrease or increase slightly. The pitch movement does not follow the high register line, an assumed top line of the speakers pitch range. H- after L* results in an increase to a middlehigh level that is reached either at one of the following stressed syllables or at the end of the accented word. Afterwards there will be a plateau reaching to the end of the intermediate phrase.
Phrase accents which function as edge tones but may also associate with stressed syllables or other tone-bearing units can now be marked with a separate L(*) or H(*) label, to indicate the secondary nature of the postnuclear prominence (cf. Grice et al., to appear). The four final and the one initial boundary tone are:
L-% Marks a larger boundary than L-. The decrease in pitch is most of-ten lower than in L- alone. After the falling movement that appears only after H accents the contour is flat along the lower register line.
On the last syllable pitch is decreasing even more below the register line (so called “final lowering”, see page 39). This boundary tone was formerly “L-L%”. It was reduced to the current version of GToBI in order to make it phonetically more transparent. When intonational phrase (IP) and intermediate phrase (ip) boundary tones would repre-sent the same pitch level, only one tone is transcribed
L-H% Following H accent tones the L-H% is a fall-rise movement. After the minimum of the fall is reached the contour stays on a low level. On the last syllable (or shortly before) there is an increase until approximately to the mid of the speakers range, by which the high register line is mostly exceeded. After L- accent tones the L-H% is a concave rising movement that starts only on the last syllable.
Chapter 3. Literature Review 3.2 Labeling Methods
Table 3.2:Inventory of pitch accents and boundary tones in GToBI.
H-% The pitch movement in % is not separable from . After the H-the level of H-the following boundary tones is increased so much that no significant decrease appears. H-% does not mark a falling movement.
Formerly “H-L%”.
H-H% After a H accent tone the H-H% will be first realized with a continuous intonation, afterwards it increases on the last syllable. The increase on the last syllable reaches the highest regions of the speakers range. H%
after a H- tone is higher than all the other H- tones. Following a L*
or H+L* the H-H% is realized with an increase high into the speakers range. The increase is convex, that is after the accented syllable there is a middlehigh increase. After the plateau an increase occurs on the last syllable up to the highest levels of the speakers range.
%H Initial high boundary tone.
The “H” in each boundary tone may also be labeled with upstep or downstep dia-critics.
The inventory of pitch accents and boundary tones in GToBI is summarized in table 3.2. Boundary tones are realized on the end of intonation phrases and determine the phrasing. However, boundary tones can also occur at the beginning of a phrase. As already mentioned in 3.2.1 the status of the phrase accent is not without problems.
In the theory of Hayes & Lahiri (1991) there is a notational addition to the system used in Pierrehumbert, namely
“The notion of the intermediate phrase has been adopted by nu-merous authors, though the term ‘intermediate’ poses a problem if for no other reason than that it makes it difficult to come up with unam-biguous abbreviations for intermediate phrase and intonation phrase.
Hayes and Lahiri (1991) suggest that the intermediate phrase is equiv-alent to the ‘phonological phrase’ of Nespor & Vogel (1986) and oth-ers. They also propose a potentially useful notational device, based
3.3 Existing approaches Chapter 3. Literature Review on Beckman and Pierrehumbert’s idea that the phrase tone is the edge tone for the phonological phrase and the boundary tone that for the in-tonational phrase; in place of Pierrehumbert’s T for phrase tone and T% for boundary tone, they write Tp and Ti respectively. A simi-lar notation is used by Grice (1995) who writes Tb for intermediate phrase edge tones (phrase tones) and TB for intonation phrase edge tones (boundary tones). However, neither notification has so far been widely adopted, and as long as there remains doubt about the proper analysis of falling nuclear accents (and more generally about the sta-tus of the phrase tone), the notational question seems likely to remain unsettled [...]” (Ladd 1996, p. 93-94).
In her thesis, Féry (1993) argues against the phrase accent in describing German intonation patterns, by claiming that “the functions it fulfills in English can be represented by the trail tone of a bitonal tone and the phrasing, which exists inde-pendently of the tonal structure anyway” (Féry, 1993, p. 72) Therefore all nuclear accents in Féry’s approach are bitonal, whereas prenuclear tones can be monotonal.
Despite the controversy about the phrase accents the GToBI model is one possibil-ity of describing German intonation within the autosegmental-metrical framework.
It has the advantages that the theoretically stated pitch accents and boundary tones are represented by concrete examples in accompanying training material (Grice &
Benzmüller, 1997) and is surface-oriented which is important for the purposes dealt with in the present thesis. Since an approach about automatic detection of prosodic events has to have explicit reference to concrete examples of these prosodic events in speech data, the GToBI model is well suited as basis for this purposes.
After having laid out the theoretical background of intonation analysis the next section will review some of the existing approaches concerning automatic prosody recognition.