Acoustic Differentiation of ip and IP Boundary Levels: Comparison of L- and L-L% in the Switchboard Corpus
Prosodic phrase boundaries, regardless of level of disjuncture, can be signaled by variation in pitch, loudness, and finalsyllable length. In an attempt to find acoustically distinctive characteristics correlated with ip (intermediate phrase) versus IP (intonation phrase) labels in a ToBI-labeled subset of the Switchboard corpus, we compared F0 drop, intensity drop, and nucleus duration in the phrase-final rime for L- and L-L% boundary labels. The results indicate no significant difference in F0 or intensity drop, but final-syllable lengthening as measured by nucleus duration differed significantly between the two boundary levels. Additionally, F0 aperiodicity associated with creaky voice was found to occur more frequently at L-L% than at L- boundaries. These results provide empirical corroboration of the statement that F0 does not reliably differentiate L- from L-L% [1], and support previous findings that degree of finalsyllable lengthening [3] and presence of creaky phonation [10] are correlated with differences in perceived level of phrasal disjuncture.