The phonetics of sociophonetics: Validating acoustic approaches to Spanish /s/

In many varieties of Spanish, syllable- and word-final /s/ is subject to a process of reduction from sibilance [s] through aspiration [h] to deletion. Sociolinguistic studies have traditionally used a three-way classification scheme on the basis of impressionistic coding; however, in the last decade, instrumental acoustic measurements have been favored. The present study examines several potential acoustic correlates of Spanish /s/ variants, including the often-used center of gravity, in their ability to faithfully represent the original perceptually-based observation of variation. The results indicate that many measurements can capture the contrast between sibilance [s] and aspiration [h]; however, fewer measurements (center of gravity after high-pass filter, skewness after high-pass filter, intensity without high-pass filter, zero crossing rate after high-pass filter, mel-frequency cepstrum coefficient 1 without high-pass filter) are also capable of detecting the contrast between aspiration [h] and deletion without making a priori assumptions about the appearance of non-zero variants. We propose that a combination of these measurements using Principal Component Analysis, which extracts the commonalities in the measurements, better represents the [s] > [h] > 0 cline than any one measurement by itself. We discuss the need for stricter evaluations of acoustic correlates of sociophonetic categories, especially regarding consonantal variation.