Rhythm and Speech Rate: A Variation Coefficient for deltaC

Abstract

The percentage of vocalic intervals (%V) and the standard deviation of consonantal intervals (deltaC) in a speech signal are two dimensions according to which languages of different rhythm classes (e.g. stress-timed, syllable-timed) seem to be differentiable on an acoustic level (Ramus et al., 1999). In this context it has been found that especially deltaC varies considerably as a function of speech rate (Barry et al., 2003 and Dellwo & Wagner,
2003).
The present paper argues that if deltaC was determined by speech rate it would describe speech rate rather than rhythm. For this reason a variation coefficient (varcoDeltaC) will be calculated in order to monitor relative deltaC variation across speech rates. Results for varcoDeltaC support the views that a) according to varcoDeltaC rhythm classes seem to be better differentiable and b) some languages tend to vary in rhythm as a function of speech rate (German, English), while the rhythm of other languages seems to be unaffected by changes in speech rate (French).