It has been assumed that tonal alignment is not contrastive in contour tones (e.g. Hyman 1988, Odden 1995, Yip 2002). However, Remijsen (2013) and DiCanio et al. (2014) have recently reported evidence for this configuration. In relation to this controversy, we report on an acoustic analysis of the tone system of Shilluk. The dataset is built around the contrast of Low vs. Early-aligned High Fall vs. Late-aligned High Fall vs. High in closed monosyllabic stems with a short vowel. The results support the hypothesis that tonal alignment is contrastive in falling contour tones in Shilluk: the two falling contours differ consistently and significantly in terms of tonal alignment, relative both to one another and to phonetically similar level-tone configurations. The falling contours do not differ significantly in terms of a number of other phonetic parameters (F0 height, size of F0 change, duration).

Shilluk is a Western Nilotic language spoken in Southern Sudan. In the study of sound systems, the Western Nilotic languages are of particular interest on account of their rich systems of suprasegmental distinctions. For example, Dinka, another Western Nilotic language, has three levels of vowel length, a voice quality distinction (modal vs. breathy), and – depending on the dialect – three or four distinctive tone patterns (Andersen 1987, Remijsen & Manyang 2009). As we shall see, Shilluk presents a similarly complex system of suprasegmental distinctions.

Ternary or three-level vowel length is typologically rare, and supporting evidence is limited. This paper presents the results of an investigation into the hypothesised case of this configuration in Shilluk. We first describe the role of vowel length in Shilluk phonology and morphology, and then report on an acoustic study in which minimal sets for vowel length (short, long, overlong) are measured for vowel duration, coda duration, vowel quality and fundamental frequency. Short, long and overlong vowels differ significantly and substantially in terms of vowel duration: 96% of the items can be classified successfully for vowel length on the basis of this measurement alone. Of the other measurements, only vowel quality is significant, and this effect is considerably smaller. The mean values for vowel duration – 68, 111 and 150 ms for short, long and overlong vowels respectively – are similar to those reported for ternary vowel length in Dinka.

It is well known that floating tones can associate both within a word and across a word boundary. In relation to floating quantity, however, there is extensive evidence for association within a word, but not across a word boundary. This research report presents evidence for the latter configuration in Shilluk, a West Nilotic language. Shilluk noun forms may end in floating quantity, and this quantity is realized only on following vocalic prefixes, that is, across a word boundary. The investigation includes a descriptive analysis of the phenomenon and a production study based on data from ten Shilluk speakers.*

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